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.Collections.Generic;
using System.Linq;
public class PictureMatching
    {
        private static int[] item;

        public static void Main(string[] args)
        {
            Input();
            Method();
            System.Console.ReadLine();
        }

        private static void Input()
        {
            item = ToIntArray(System.Console.ReadLine().Split(' '));
        }

        private static void Method()
        {
            System.Console.WriteLine(item.Aggregate(Gcd));
        }

        private static int Gcd(int x, int y)
        {
            return y == 0 ? x : Gcd(y, x % y);
        }

        private static int[] ToIntArray(string[] str)
        {
            IEnumerable<int> intArray = str.Select(x => int.Parse(x));
            return intArray.ToArray();
        }
}