Problem Description

The number S is called the mean of two numbers R1 and R2 if S is equal to (R1+R2)/2. Mirko's birthday present for Slavko was two integers R1 and R2. Slavko promptly calculated their mean which also happened to be an integer but then lost R2! Help Slavko restore R2.

Input Format

The first and only line of input contains two integers R1 and S, both between -1000 and 1000.

Output Format

Output R2 on a single line.

Sample Input and Output

Sample Input #1

11 15

Sample Output #1

19

Sample Input #2

4 3

Sample Output #2

2

见题面 Input 部分

见题面 Output 部分