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 Greatest_Common_Divisor
{
  public static void Main()
  {
    string str_num = Console.ReadLine();
    string[] sp_num = str_num.Split();
    int x = int.Parse(sp_num[0]);
    int y = int.Parse(sp_num[1]);
    int q = x%y;
    
    while(q!=0)
    {
      x = y; 
      y = q;
      q = x%y;
    }
    
    Console.WriteLine(y);
  }
}