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 B
{
	static void Main()
	{
		var h = Array.ConvertAll(Console.ReadLine().Split(), int.Parse);
		Console.WriteLine(Gcd(h[0], h[1]));
	}

	static int Gcd(int a, int b) { for (int r; (r = a % b) > 0; a = b, b = r) ; return b; }
}