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;
using System.Collections;
using System.Collections.Generic;

class Program
{
    static long GCD(long a, long b)
    {
        return (a < b)? GCD(b, a):
               (a % b == 0)? b:
               GCD(b, a % b);
    }
    public static void Main(string[] args)
    {
        string[] s = Console.ReadLine().Split();
        long A = long.Parse(s[0]);
        long B = long.Parse(s[1]);
        Console.WriteLine(GCD(A, B));
    }
}