题解 | #牛牛的等差数列#

import java.util.Scanner;
public class Main {
    public static void main(String[] args) {
        Scanner scanner = new Scanner(System.in);
        int a = scanner.nextInt();
        int b = scanner.nextInt();
        System.out.println(b - a + b);// 2 * b - a
    }
}