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 AOJ
{
	public static void Main()
	{
		var input = Console.ReadLine().Trim().Split(' ');
		int a = int.Parse(input[0]);
		int b = int.Parse(input[1]);
		int large = Math.Max(a, b);
		int small = Math.Min(a, b);
		if(small == 0)
		{
			Console.WriteLine(small);
			return;
		}

		while(true)
		{
			int mod = large % small;
			if(mod == 0)
			{
				Console.WriteLine(small);
				break;
			}
			large = small;
			small = mod;
		}
	}
}