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;
using System.Linq;

namespace ALDS1_1_B{
    class Sample{
        static void Main(string[] args){
            int[] nums = Console.ReadLine().Trim().Split(' ').Select(x => int.Parse(x)).ToArray();
            Console.WriteLine(Gcd(nums[0], nums[1]));
        }
        static int Gcd(int num1, int num2){
            if(num1 < num2) {
                return Gcd(num2, num1);
            }

            while(num2 != 0){
                var remainder = num1 % num2;
                num1 = num2;
                num2 = remainder;
            }
            return num1;
        }
    }
}