The number ~S~ is called the mean of two numbers ~R_1~ and ~R_2~ if ~S~ is equal to ~\frac{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 Specification

The first and only line of input contains two integers ~R_1~ and ~S~, both between ~-1\,000~ and ~1\,000~.

Output Specification

Output ~R_2~ on a single line.

Sample Input 1

11 15

Sample Output 1

19

Sample Input 2

4 3

Sample Output 2

2