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[] s = Console.ReadLine().Split(' ');
        int x = int.Parse(s[0]);
        int y = int.Parse(s[1]);

        Console.WriteLine(GCDivisor(x,y));
    }

    static int GCDivisor(int x, int y)
    {
        int n = Math.Min(x, y);
        int d = 0;
        for(d = n;d > 0; d--)
        {
            if (x % d == 0 && y % d == 0)
                break;
        }
        return d;
    }
}