Problem:
Score : 100 points

Problem Statement

Takahashi is a user of a site that hosts programming contests.

When a user competes in a contest, the rating of the user (not necessarily an integer) changes according to the performance of the user, as follows:

Let the current rating of the user be a.

Suppose that the performance of the user in the contest is b.

Then, the new rating of the user will be the avarage of a and b.

For example, if a user with rating 1 competes in a contest and gives performance 1000, his/her new rating will be 500.5, the average of 1 and 1000.

Takahashi's current rating is R, and he wants his rating to be exactly G after the next contest.

Find the performance required to achieve it.

Constraints

0 \leq R, G \leq 4500

All input values are integers.

Input

Input is given from Standard Input in the following format:

R
G

Output

Print the performance required to achieve the objective.

Sample Input 1

2002
2017

Sample Output 1

2032

Takahashi's current rating is 2002.

If his performance in the contest is 2032, his rating will be the average of 2002 and 2032, which is equal to the desired rating, 2017.

Sample Input 2

4500
0

Sample Output 2

-4500

Although the current and desired ratings are between 0 and 4500, the performance of a user can be below 0.

Solution in Java8 (OpenJDK 1.8.0) (judge verdict: Wrong Answer)

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

public class Main {
    
    class Answer {
        int N, K;
        
        public long solve() {
            long min = 1;
            for (int i = 0; i < N; i++) {
                min = Math.min(min*2, min+K);
            }
            return min;
        }
        
        public void main(FastScanner in, PrintWriter out) {
            N = in.nextInt();
            K = in.nextInt();
            out.println( solve() );
        }
        
        public void p(Object o) { System.out.print(o); }
        public void pl(Object o) { System.out.println(o); }
        public void arp(int[] o) { pl( Arrays.toString(o) ); }
        public void arpp(int[][] o) { 
            for (int i = 0; i < o.length; i++) {
                for (int j = 0; j < o[0].length; j++) { p(o[i][j] + " "); }
                pl("");
            }
        }
        public void ck(Object o1, Object o2) { pl(o1 + " " + o2); }
        public void ckk(Object o1, Object o2, Object o3) { pl(o1 + " " + o2 + " " + o3); }
        public void ckkk(Object o1, Object o2, Object o3, Object o4) { 
            pl(o1 + " " + o2 + " " + o3 + " " + o4);
        }
    }

    public static void main(String[] args) throws Exception {
        InputStream inputStream = System.in;
        OutputStream outputStream = System.out;
        FastScanner in = new FastScanner(inputStream);
        PrintWriter out = new PrintWriter(outputStream);
        Main problem = new Main();
        Answer ans = problem.new Answer();
        ans.main(in, out);
        out.close();
        in.close();
    }
    
    static class FastScanner {
        BufferedReader br;
        StringTokenizer st;
        public FastScanner(InputStream in) { br = new BufferedReader(new InputStreamReader(in)); }
        public int nextInt() { return Integer.parseInt(next()); }
        public long nextLong() { return Long.parseLong(next()); }
        public double nextDouble() { return Double.parseDouble(next()); }
        public String next() {
            while (st == null || !st.hasMoreTokens()) {
                try { st = new StringTokenizer(br.readLine()); } 
                catch (IOException e) { e.printStackTrace(); }
            }
            return st.nextToken();
        }
        public String nextLine() {
            String str = "";
            try { str = br.readLine();
            } catch (IOException e) { e.printStackTrace(); }
            return str;
        }
        public void close() throws IOException { br.close(); }
    }
}