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 JAVA (judge verdict: Accepted)

import java.util.Scanner;

public class Main {

    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        int[] a = new int[]{sc.nextInt(), sc.nextInt()};
        int big, small;
        if (a[0] == a[1]) {
            System.out.println(a[0]);
            return;
        } else if (a[0] > a[1]) {
            big = a[0];
            small = a[1];
        } else {
            big = a[1];
            small = a[0];
        }

        while (true) {
            int x = big % small;
            if (x == 0) {
                System.out.println(small);
                return;
            } else {
                big = small;
                small = x;
            }
        }
    }
}