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;

class Program
{
    static void Main()
    {
        string[] input = Console.ReadLine().Split(' ');
        Console.WriteLine(Solve(int.Parse(input[0]),int.Parse(input[1])));
    }
    static int Solve(int a, int b)
    {
        int small,mod;
        if(a>b){
            small=b;
            mod=a%b;
        }else{
            small=a;
            mod=b%a;
        }
        if (mod == 0) return small;
        else return Solve(small, mod);
    }
}