Mean arithmetic

Petrik has two numbers $a$ and $b$ ($a\le b$). He found the arithmetic mean of these numbers (let it be the number $c$), which turned out to be an integer. That is, $c=\frac{a+b}{2}$.

You are given the number $a$ (i.e. the smaller of the two numbers), as well as the number $c$. Find $b$.

Input

The first line contains an integer $a$ ($1\le a\le 100$).

The second line contains an integer $c$ ($a\le c\le 100$).

Output

Output one integer — $b$.

Examples