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 Program
{
    static void Main()
    {
        string[] s = Console.ReadLine().Split(' ');
        int a = int.Parse(s[0]);
        int b = int.Parse(s[1]);
        
        int x=0;
        
        if (a < b) { x = a; a = b; b = x; }
        while (b != 0)
        {
           x = b;
           b = a % x;
           a = x;
        }
        
        Console.WriteLine(x);
    }
}