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 C++14 (GCC 5.4.1) (judge verdict: Accepted)

#include <iostream>
#include <string>
#include <algorithm>
#include <functional>
#include <vector>
#include <stack>
#include <queue>
#include <deque>
#include <set>
#include <map>
#include <cstdio>
#include <cmath>
#include <tuple>
#include <iomanip>
#include <numeric>
#include <unordered_map>
#include <sstream>   
#include<limits.h>
#include<float.h>
#include<list>
#include <array>
#include <complex>
using namespace std;
#define i64  long long
#define int  long long
 
#define I32_MAX 2147483647
#define I64_MAX 9223372036854775807LL
#define I64_MAX2 1223372036854775807LL
#define INF I64_MAX2
#define MOD 1000000007
#define MEM_SIZE 10000

// int DP[MEM_SIZE][MEM_SIZE] = {0};
// int GMEM[MEM_SIZE][MEM_SIZE] = {0};
template<typename T> void DEBUG(T e){std::cout << e << std::endl;}
template<class T> void DEBUG(string str, T e){std::cout <<str << ">>" << e << std::endl;}
template<typename T> void DEBUG(const std::vector<T>& v){for(const auto& e : v){ std::cout << e << " "; } std::cout << std::endl;}
template<typename T> void DEBUG(const std::vector<std::vector<T> >& vv){ for(const auto& v : vv){ DEBUG(v); } }
template <class T> void corner(bool flg, T hoge) {if (flg) {cout << hoge << endl; exit(0);}}
template< typename T1, typename T2 > inline bool chmax(T1 &a, T2 b) { return a < b && (a = b, true); }
template< typename T1, typename T2 > inline bool chmin(T1 &a, T2 b) { return a > b && (a = b, true); }
template<typename T> void SORT_(std::vector<T>& v,bool GREATER = 0){if(GREATER == 0)sort(v.begin(),v.end());else{sort(v.begin(),v.end(),std::greater<T>());}}

void solve(void)
{
  int A,B;
  cin>>A>>B;
  cout<<A + (B-A)*2<<endl;
  
  

  return;

   
}


int32_t main(int32_t argc, const char *argv[])
{
  std::ios::sync_with_stdio(false);
  std::cin.tie(0);

  std::cout << std::fixed;
  std::cout << std::setprecision(9);
  solve();

 
  return 0;
}