题解 | #牛牛的等差数列#

import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStreamReader;
public class Main{
    public static void main(String[] args) throws IOException{
        BufferedReader bf = new BufferedReader(new InputStreamReader(System.in));
        String str[] = bf.readLine().split(" ");
        int a = Integer.parseInt(str[0]);
        int b = Integer.parseInt(str[1]);
        int x = b-a;
        int c = b+x;
        System.out.println(c);
    }
}