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 Ex160424_1{
    public class Program{
        public static void Main(string[] args){
            var input = Console.ReadLine().Split(' ');
            var x = int.Parse(input[0]);
            var y = int.Parse(input[1]);

            Func<int, int, int> gcd = null;
            gcd = (i, j) =>{
                if(j == 0) return i;
                return gcd(j, i % j);
            };

            Console.WriteLine(gcd(Math.Max(x, y), Math.Min(x, y)));
        }
    }
}