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;

namespace GCD
{
    internal class Program
    {
        public static void Main(string[] args)
        {
            var input = Console.ReadLine().Split(' ').Select(int.Parse).ToArray();
            Console.WriteLine(Gcd(input[0], input[1]));
        }

        static int Gcd(int m, int n)
        {
            if (m <= n)
            {
                var tmp = m;
                m = n;
                n = tmp;
            }

            while (m % n != 0)
            {
                var tmp = n;
                n = m % n;
                m = tmp;
            }

            return n;
        }
    }
}