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 procon
{
    public class Program
    {
        public static void Main(string[] args)
        {
            var inputs = Console.ReadLine().Split().Select(int.Parse).ToArray();
            var x = inputs[0];
            var y = inputs[1];
            
            var min = Math.Min(x, y);
            var max = Math.Max(x,y);
            var mod = max%min;
            while(mod != 0)
            {
                max = Math.Max(min, mod);
                min = Math.Min(min, mod);
                mod = max % min;
            }

            Console.WriteLine(min);
        }
    }
}