java 3046

import java.io.*;
import java.util.StringTokenizer;

public class Main {

    public static void main(String[] args)throws IOException {

        BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
        StringTokenizer st = new StringTokenizer(br.readLine());

        //변수 중 하나
        int R1 = Integer.parseInt(st.nextToken());
        //(R1 + R2) / 2 = S
        int S = Integer.parseInt(st.nextToken());
        // S * 2 - R1 = R2
        int R2 = (S*2)-R1;

        System.out.println(R2);
        
        br.close();
    }
}