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.*;
import java.util.stream.*;
class Main {
    public static void main(String[] args) {
        Scanner input = new Scanner(System.in);
        long x,y;
        x = input.nextLong();
        y = input.nextLong();
        long ans;
        ans = GCD(x,y);
        System.out.println(ans);
    }
    public static long GCD(long a, long b){
        long tmp,gcd;
        while (a != 0 && b != 0){
            if (a < b){
                tmp = a;
                a = b;
                b = tmp;
            }
            tmp = a;
            a = b;
            b = tmp%b;
        }
        gcd = Math.max(a,b);
        return gcd;
    }
}