Contest Duration: - (local time) (100 minutes) Back to Home
A - Rating Goal /

Time Limit: 2 sec / Memory Limit: 256 MB

### 問題文

ここでは, コンテストに出場した時にこの順位に応じて「パフォーマンス」というものがつき、それによってレーティング (整数とは限らない) が次のように変化します。

• 現在のレーティングを a とする。
• 次のコンテストで, パフォーマンス b を取ったとする。
• そのとき, レーティングは ab の平均まで変化する。

そのとき, 高橋君が取るべきパフォーマンスを求めなさい。

### 制約

• 0 \leq R, G \leq 4500
• 入力はすべて整数

### 入力

R
G


### 入力例 1

2002
2017


### 出力例 1

2032


### 入力例 2

4500
0


### 出力例 2

-4500


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.