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_B
{
    class Program
    {
        static void Main(string[] args)
        {
            var a = Array.ConvertAll(Console.ReadLine().Split(' '), int.Parse);
            Console.WriteLine(gcd(a[0],a[1]));
        }

        static int gcd(int a, int b)
        {
            return a % b == 0 ? b : gcd(b, a % b);
        }
    }
}