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{
    public static void Main(){
        var s=Console.ReadLine().Split(' ');
        var a=int.Parse(s[0]);
        var b=int.Parse(s[1]);
        while(a%b!=0){
            var tmp=b;
            b=a%b;
            a=tmp;
        }
        Console.WriteLine(b);
    }
}