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;

class ALDS1_1A
{
    static void Main()
    {
        string str = Console.ReadLine();
        int a = int.Parse(str.Split(' ')[0]);
        int b = int.Parse(str.Split(' ')[1]);
        int c;
        if (a < b)
        {
            c = a; a = b; b = c;
        }
        while (true)
        {
            c = a % b;
            if (c == 0) break;
            a = b;
            b = c;
        }
        Console.WriteLine(b);
    }
}