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 Ex160424_1{
    public class Program{
        public static void Main(string[] args){
            var i = Console.ReadLine().Split(' ').Select(int.Parse).ToArray();

            Action<int, int> gcd = null;
            gcd = (x, y) =>{
                if(y == 0) Console.WriteLine(x);
                else gcd(y, x % y);
            };
            gcd(i[0], i[1]);
        }
    }
}