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 ALDS1_1_A
{
    class Program
    {
        static void Main(string[] args)
        {
            // B
            string[] data = System.Console.ReadLine().Split(' ');
            var A = System.Int32.Parse(data[0]);
            var B = System.Int32.Parse(data[1]);
            var res = gcd(A, B);
            System.Console.WriteLine(res);
        }

        static int gcd(int x, int y) {
            if (y==0) return x;
            else {
                if (x >= y) return gcd(y, x % y);
                else return gcd(x, y % x);
            }
        }
    }
}