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.Linq;

class Program
{
    static void Main(string[] args) {
        int[] s = Console.ReadLine().Split().Select(int.Parse).ToArray();
        int x = s[0];
        int y = s[1];
        Console.WriteLine(gcd(x,y));
    }
    static int gcd(int x, int y) {
        if (x<y) return gcd(y,x);
        while(x%y>0) {
            int temp = y;
            y = x%y;
            x = temp;
        }
        return y;
    }
}