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;
using System.Collections.Generic;

class main{
    public static void Main(String[] args){
        int[] a = Array.ConvertAll(Console.ReadLine().Split(' '),int.Parse);

        Console.WriteLine(gcd(a[0],a[1]));
    }

    internal static int gcd(int x,int y){
        if(x < y){
            Swap(x,y);
        }

        while(y > 0){
            int r = x % y;
            x = y;
            y = r;
        }

        return x;
    }

    internal static void Swap(int a, int b) {
        var t = a;
        a = b;
        b = t;
    }
}