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;

namespace GCD
{
    class Program
    {
        private static int Gcd(int a, int b)
        {
            if (a < b)
            {   
                int t = a;
                a = b;
                b = t;
            }
            int c = a % b;
            return c == 0 ? b : Gcd(b, c);
        }
        static void Main()
        {
            int[] i = Array.ConvertAll(Console.ReadLine().Split(), int.Parse);
            Console.WriteLine(Gcd(i[0], i[1]));
        }
    }
}