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 MyClass
{
    static void Main(string[] args)
    {
        string[] str = Console.ReadLine().Split(' ');
        int a = int.Parse(str[0]);
        int b = int.Parse(str[1]);
        do
        {
            if (a < b)
            {
                int t = b;
                b = a;
                a = t;
            }
            else
            {
                a = a % b;
            }
        } while (b != 0);
        Console.WriteLine(a);
    }
}