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)

#pragma warning disable
using System.Collections.Generic;
using System.IO;
using System.Linq;
using System;
class E { static void Main() { new J(); } }
class J
{
	//int F => int.Parse(Console.ReadLine());
	int[] G() { return Console.ReadLine().Split().Select(_ => int.Parse(_)).ToArray(); }
	public J()
	{
		//Console.SetOut(new StreamWriter(Console.OpenStandardOutput()) { AutoFlush = false });
		var I = G();
		Console.WriteLine(GCD(I[0], I[1]));
		//Console.Out.Flush();
	}
	int GCD(int n, int m)
	{
		var a = Math.Abs(n);
		var b = Math.Abs(m);
		if (a < b) { var c = a; a = b; b = c; }
		while (b > 0)
		{
			var c = a % b;
			a = b;
			b = c;
		}
		return a;
	}
}