题解 | #牛牛的等差数列#

import java.util.Scanner;

// 注意类名必须为 Main, 不要有任何 package xxx 信息
public class Main {
    public static void main(String[] args) {
        Scanner in = new Scanner(System.in);
        
            int a = in.nextInt();
            int b = in.nextInt();
            System.out.println(b+(b-a));
        
    }
}