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)

// Getting Started - Gratest Common Divisor
// http://judge.u-aizu.ac.jp/onlinejudge/description.jsp?id=ALDS1_1_B
using System;
using System.Linq;

namespace ALDS1_1_B {
	class Program {
		public Program() {}
		
		public static void Main() {
			new Program().Calc();
		}
		
		void Calc() {
			var A = Input				// Array : x, y
					.Split(' ')
					.Select(i => int.Parse(i))
					.ToArray();
			
			Output(gcd(A).ToString());
		}
		
		String Input {
			get {
				return Console.ReadLine();
			}
		}
		
		void Output(String str) {
			Console.WriteLine(str);
		}
		
		int gcd(int[] A) {
			return A[1] == 0 ? A[0] : gcd(new int[] {A[1], A[0] % A[1]});
		}
	}
}