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BOJ_18352.java
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BOJ_18352.java
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import java.io.BufferedReader;
import java.io.InputStreamReader;
import java.util.*;
public class Main {
static BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
static final int INF = -1;
public static void main(String[] args) throws Exception {
new Main().solution();
}
private void solution() throws Exception {
StringTokenizer st = new StringTokenizer(br.readLine());
int n = Integer.parseInt(st.nextToken());
int m = Integer.parseInt(st.nextToken());
int k = Integer.parseInt(st.nextToken());
int x = Integer.parseInt(st.nextToken());
List<Integer>[] edges = new List[n+1];
for (int i = 1; i <= n; i++) edges[i] = new ArrayList<>();
for (int i = 0; i < m; i++) {
st = new StringTokenizer(br.readLine());
int a = Integer.parseInt(st.nextToken());
int b = Integer.parseInt(st.nextToken());
edges[a].add(b);
}
int[] dist = new int[n+1];
Arrays.fill(dist, INF);
Queue<Integer> q = new ArrayDeque<>();
q.add(x);
dist[x] = 0;
List<Integer> answer = new ArrayList<>();
while (!q.isEmpty()) {
int cur = q.poll();
if (dist[cur] > k) break;
if (dist[cur] == k) answer.add(cur);
for (int next : edges[cur]) {
if (dist[next] != INF) continue;
dist[next] = dist[cur]+1;
q.add(next);
}
}
Collections.sort(answer);
StringBuilder sb = new StringBuilder();
for (int cur : answer) {
sb.append(cur).append('\n');
}
System.out.print(answer.isEmpty() ? -1 : sb);
}
}