Problem:
Greatest Common Divisor

Write a program which finds the greatest common divisor of two natural numbers a and b

Input

a and b are given in a line sparated by a single space.

Output

Output the greatest common divisor of a and b.

Constrants

1 ≤ a, b ≤ 109

Hint

You can use the following observation:

For integers x and y, if x ≥ y, then gcd(x, y) = gcd(y, x%y)

Sample Input 1

54 20

Sample Output 1

2

Sample Input 2

147 105

Sample Output 2

21

Solution in C# (judge verdict: Accepted)

using System;
class gcd{
  public static void Main(){
    String[] str = Console.ReadLine().Split(' ');
    int n = int.Parse(str[0]);
    int m = int.Parse(str[1]);
    if(m > n){
      int temp = n;
      n = m;
      m = temp;
    }
    while(true){
      if(n%m == 0){
        break;
      }
      else{
        int a = n/m;
        int b = n - m*a;
        n = m;
        m = b;
      }
    }
    Console.WriteLine(m);
  }
}