Problem Statement

The window of Takahashi's room has a width of $A$. There are two curtains hung over the window, each of which has a horizontal length of $B$. (Vertically, the curtains are long enough to cover the whole window.)

We will close the window so as to minimize the total horizontal length of the uncovered part of the window. Find the total horizontal length of the uncovered parts of the window then.

Constraints

• $1 \leq A \leq 100$
• $1 \leq B \leq 100$
• $A$ and $B$ are integers.

Input

Input is given from Standard Input in the following format:

A B

Output

Print the total horizontal length of the uncovered parts of the window.