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);}}