diff --git a/chris-an/home/3.11/Boj_10872.java b/chris-an/home/3.11/Boj_10872.java
new file mode 100644
index 00000000..22c4961d
--- /dev/null
+++ b/chris-an/home/3.11/Boj_10872.java
@@ -0,0 +1,16 @@
+import java.util.Scanner;
+
+public class Boj_10872 {
+
+    static int value = 1;
+    public static int factorial(int n) {
+        if (n == 0) return value;
+        value *= n ;
+        return factorial(n-1);
+    }
+
+    public static void main(String[] args) {
+        Scanner sc = new Scanner(System.in);
+        System.out.println(factorial(sc.nextInt()));
+    }
+}
diff --git a/chris-an/home/3.11/Boj_1676.java b/chris-an/home/3.11/Boj_1676.java
new file mode 100644
index 00000000..8438aade
--- /dev/null
+++ b/chris-an/home/3.11/Boj_1676.java
@@ -0,0 +1,44 @@
+import java.io.BufferedReader;
+import java.io.IOException;
+import java.io.InputStreamReader;
+
+
+public class Boj_1676 {
+    public static void main(String[] args) throws IOException {
+        BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
+        int n = Integer.parseInt(br.readLine());
+        int cnt = 0;
+        for (int i = 5; i <= n ; i *= 5) {
+            cnt += n / i;
+        }
+
+        System.out.println(cnt);
+    }
+}
+
+/*
+
+public class Main {
+
+    static int value = 1;
+
+    public static int factorial(int n) {
+        if (n == 0) return value;
+        value *= n;
+        return factorial(n - 1);
+    }
+
+    public static void main(String[] args) {
+        Scanner sc = new Scanner(System.in);
+        int N = factorial(sc.nextInt());
+        char [] ch = Integer.toString(N).toCharArray();
+
+        int cnt = 0;
+        for (int i = ch.length-1; i > 0; i--) {
+            if (ch[i] == '0') cnt++;
+            else break;
+        }
+        System.out.println(cnt);
+    }
+}
+ */
\ No newline at end of file
diff --git a/chris-an/home/3.11/Boj_6588.java b/chris-an/home/3.11/Boj_6588.java
new file mode 100644
index 00000000..70089008
--- /dev/null
+++ b/chris-an/home/3.11/Boj_6588.java
@@ -0,0 +1,91 @@
+import java.io.*;
+import java.util.Arrays;
+
+
+public class Boj_6588 {
+    static boolean [] targetNumbers;
+    public static void isPrime() {
+        targetNumbers = new boolean[1000001];
+
+        Arrays.fill(targetNumbers, true);
+//        for(int i=2;i<=N;i++) {
+//            targetNumbers[i] = true;
+//        }
+        for (int i = 2; i<=1000000; i++) {
+            // 이미 확인된 건 넘기기
+            if (!targetNumbers[i]) continue;
+            // 배수 출발.
+            for (int j = i * 2; j <= 1000000; j += i ) targetNumbers[j] = false;
+        }
+    }
+    public static void main(String[] args) throws IOException {
+
+
+        BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
+        BufferedWriter bw = new BufferedWriter(new OutputStreamWriter(System.out));
+        isPrime();
+        while (true) {
+            int n = Integer.parseInt(br.readLine());
+            if (n == 0) break;
+
+            int primeNum = Integer.MIN_VALUE;
+            for (int i = 2; i <= n/2; i++) {
+                if (targetNumbers[i] && targetNumbers[n-i]) {
+                    primeNum = i;
+                    break;
+                }
+            }
+
+            if (primeNum > 0) bw.write(n + " = " + primeNum + " + " + (n-primeNum) + "\n");
+            else bw.write("Goldbach's conjecture is wrong.\n");
+        }
+        bw.flush();
+        bw.close();
+        br.close();
+    }
+}
+
+
+/*
+
+ 시간 초과.
+
+public class Main {
+    public static String isPrime(int n) {
+        ArrayList<Integer> list = new ArrayList<>();
+        boolean [] prime = new boolean[n+1];
+        Arrays.fill(prime, true);
+        prime[0] = prime[1] = false;
+        for (int i = 2; i <= Math.sqrt(prime.length); i++) {
+            if (prime[i]) {
+                for (int j = i*i; j <= n; j+=i) prime[j] = false;
+            }
+        }
+        for (int i = 2; i < n; i++) {
+            if (true == prime[i]) {
+                list.add(i);
+            }
+        }
+        for (int i = 0; i < list.size(); i++) {
+            for (int k = i; k < list.size(); k++) {
+                if (list.get(i)+list.get(k) == n) {
+                    return n + " = " + list.get(i) + " + " + list.get(k);
+                }
+            }
+        }
+        return "Goldbach's conjecture is wrong.";
+    }
+
+    public static void main(String[] args) throws IOException {
+        BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
+        int stop = 1;
+        while (stop != 0) {
+            stop = Integer.parseInt(br.readLine());
+            if (stop!=0) {
+                System.out.println(isPrime(stop));
+            }
+        }
+    }
+}
+
+ */
diff --git a/chris-an/office/3.08/Programmers_42840.java b/chris-an/office/3.08/Programmers_42840.java
new file mode 100644
index 00000000..7aab610c
--- /dev/null
+++ b/chris-an/office/3.08/Programmers_42840.java
@@ -0,0 +1,2 @@
+public class Programmers_42840 {
+}
diff --git a/chris-an/office/3.10/Programmers_42839.java b/chris-an/office/3.10/Programmers_42839.java
new file mode 100644
index 00000000..3ac7a184
--- /dev/null
+++ b/chris-an/office/3.10/Programmers_42839.java
@@ -0,0 +1,51 @@
+import java.io.BufferedReader;
+import java.io.IOException;
+import java.io.InputStreamReader;
+import java.util.Arrays;
+import java.util.HashSet;
+
+public class Programmers_42839 {
+
+    static HashSet<String> hs = new HashSet<>();
+
+    public static void recur(String candidate, String remain) {
+        // base case 라고 불림.
+        if (!candidate.equals("")) hs.add(candidate);
+        for (int i = 0; i < remain.length(); i++){
+            recur(candidate + remain.charAt(i), remain.substring(0, i) + remain.substring(i+1));
+        }
+    }
+
+    public static boolean isPrime(int n) {
+        // 0, 1 는 제외
+        if (n < 2) return false;
+        // true = 소수, false = 합성수
+        boolean [] prime = new boolean[n+1];
+        Arrays.fill(prime, true);
+
+        prime[0] = prime[1] = false;
+        for (int i = 2; i*i <= n; i++) {
+            // 소수가 아니라면?
+            if (prime[i]) {
+                for (int j = i*i; j <= n; j+=i) prime[j] = false;
+            }
+        }
+        return prime[n];
+    }
+
+    public static void main(String[] args) throws IOException {
+        BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
+        String str = br.readLine();
+
+        recur("", str);
+        int cnt = 0;
+
+        for (String s : hs) {
+            if (isPrime(Integer.parseInt(s)))
+                cnt++;
+        }
+
+        System.out.println(cnt);
+
+    }
+}
diff --git a/chris-an/office/3.10/Programmers_42842.java b/chris-an/office/3.10/Programmers_42842.java
new file mode 100644
index 00000000..29a47e7c
--- /dev/null
+++ b/chris-an/office/3.10/Programmers_42842.java
@@ -0,0 +1,38 @@
+import java.io.BufferedReader;
+import java.io.IOException;
+import java.io.InputStreamReader;
+
+public class Programmers_42842 {
+    
+    public static int [] solution(int brown, int yellow) {
+        /*
+        int a = brown/2 + 2;
+        int b = yellow + brown;
+
+        double alpha = (a+Math.sqrt(a*a - 4*b)) / 2;
+        double beta = a - alpha;
+
+        int [] answer = {(int) alpha, (int) beta};
+        */
+
+        int[] answer = new int[2];
+
+        for(int i = 1; i <= yellow; i++) {
+            if(yellow % i == 0) {
+                if(2 * i + (2 * yellow / i) == brown - 4) {
+                    answer[0] = i + 2;
+                    answer[1] = yellow / i + 2;
+                }
+            }
+        }
+        return answer;
+    }
+    public static void main(String[] args) throws IOException {
+        BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
+        String [] ch = br.readLine().split(" ");
+        int b = Integer.parseInt(ch[0]);
+        int y = Integer.parseInt(ch[1]);
+
+        System.out.println(solution(b,y)[0] +" " + solution(b,y)[1]);
+    }
+}
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