The number $S$ is called the mean of two numbers $R_1$ and $R_2$ if $S$ is equal to $(R_1+R_2)/2$. Mirko’s birthday present for Slavko was two integers $R_1$ and $R_2$. Slavko promptly calculated their mean which also happened to be an integer but then lost $R_2$! Help Slavko restore $R_2$.

-----Input-----
The first and only line of input contains two integers $R_1$ and $S$, both between $-1000$ and $1000$.

-----Output-----
Output $R_2$ on a single line.

-----Examples-----
Sample Input:
11 15
Sample Output:
19

Difficulty: introductory

Starter code:

Solutions: