100760: [AtCoder]ABC076 A - Rating Goal

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 $0$.