解题思路：

找规律

最大的最小公因数就是两数的差值
5 7  gcd=2   
1 3  gcd=2
1 4   gcd=3

import java.util.Scanner;

public class Main {
       public static void main(String[] args) {
        Scanner scan = new Scanner(System.in);
        long a = scan.nextLong();
        long b = scan.nextLong();
        long c = Math.abs(a - b);
        long k = 0;

        //逆推
        k = c - (a % c);
        System.out.println(k);
    }
    
}