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 static System.Console;

namespace AOJ
{
    public class ALDS1_1_B
    {
        public static void Main(string[] args)
        {
            string[] input = ReadLine().Split(' ');
            int a = int.Parse(input[0]);
            int b = int.Parse(input[1]);

            WriteLine(GreatestCommonDivisor((uint)a,(uint)b));
        }

        public static uint GreatestCommonDivisor(uint x, uint y)
        {
            while (x != 0 && y != 0)
            {
                if (x > y) x %= y; else y %= x;
            }

            return x == 0 ? y : x;
        }
    }
}