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: Time Limit Exceeded)

using System;

namespace ALDS1_1_B
{
    class Program
    {
        static void Main(string[] args)
        {
            var input = (Console.ReadLine().Split(' '));
            int x = Int32.Parse(input[0]);
            int y = Int32.Parse(input[1]);
            Console.WriteLine("{0}", calcGCD(x, y));
        }

        static string calcGCD(int x, int y)
        {
            for (int i = Math.Min(x, y); i >= 2; i--)
            {
                if (x % i == 0 && y % i == 0) { return i.ToString(); }
            }
            return "1";
        }
    }
}