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.Text;

namespace GCD
{
    class Program
    {
        static void Main(string[] args)
        {
            var splitInput = Console.ReadLine().Split();

            var x = int.Parse(splitInput[0]);
            var y = int.Parse(splitInput[1]);

            if (x < y)
            {
                int temp = x;
                x = y;
                y = temp;
            }

            int rem = 0;

            while (true)
            {
                rem = x % y;

                if (rem == 0)
                    break;

                x = y;
                y = rem;
            } 

            Console.WriteLine(y);
        }
    }
}