diff --git a/Algorithms/Math/Fibonacci.fs b/Algorithms/Math/Fibonacci.fs
index 1fb284a..32e8682 100644
--- a/Algorithms/Math/Fibonacci.fs
+++ b/Algorithms/Math/Fibonacci.fs
@@ -1,7 +1,13 @@
-namespace Algorithms.Math
+namespace Algorithms.Math
 
 module Fibonacci =
     let rec PrintSerie (one: int) (two: int) =
         let fibo = one + two
         System.Console.WriteLine fibo
-        PrintSerie two fibo
\ No newline at end of file
+        PrintSerie two fibo
+        
+    let rec NthFibonacci (n: int): int =
+        match n with
+            | 0 -> 0
+            | 1 -> 1
+            | n -> NthFibonacci (n-1) + NthFibonacci (n-2)
diff --git a/Algorithms/Math/Greatest_Common_Divisor.fs b/Algorithms/Math/Greatest_Common_Divisor.fs
new file mode 100644
index 0000000..91cf8f0
--- /dev/null
+++ b/Algorithms/Math/Greatest_Common_Divisor.fs
@@ -0,0 +1,7 @@
+namespace Algorithms.Math
+
+module GreatestCommonDivisor =
+    let rec gcd (m: int) (n: int): int = 
+      match m,n with
+        | 0,n -> n
+        | m,n -> gcd (n % m) m
diff --git a/Algorithms/Math/PerfectNumbers.fs b/Algorithms/Math/Perfect_Numbers.fs
similarity index 100%
rename from Algorithms/Math/PerfectNumbers.fs
rename to Algorithms/Math/Perfect_Numbers.fs
diff --git a/README.md b/README.md
index d03ca7b..7f0faf1 100644
--- a/README.md
+++ b/README.md
@@ -11,6 +11,7 @@ This repository contains algorithms and data structures implemented in F# for ed
     + [Abs Minimum](https://github.com/TheAlgorithms/F-Sharp/blob/main/Algorithms/Math/AbsMin.fs)
     + [Factorial](https://github.com/TheAlgorithms/F-Sharp/blob/main/Algorithms/Math/Factorial.fs)
     + [Fibonacci](https://github.com/TheAlgorithms/F-Sharp/blob/main/Algorithms/Math/Fibonacci.fs)
+    + [Greatest Common Divisor](https://github.com/TheAlgorithms/F-Sharp/blob/main/Algorithms/Math/Greatest_Common_Divisor.fs)
     + [Perfect Numbers](https://github.com/TheAlgorithms/F-Sharp/blob/main/Algorithms/Math/Perfect_Numbers.fs)
     + [Power](https://github.com/TheAlgorithms/F-Sharp/blob/main/Algorithms/Math/Power.fs)
   + [Search](https://github.com/TheAlgorithms/F-Sharp/tree/main/Algorithms/Search)