Score : $100$ points
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.
Input is given from Standard Input in the following format:
Print the total horizontal length of the uncovered parts of the window.
We have a window with a horizontal length of $12$, and two curtains, each of length $4$, that cover both ends of the window, for example. The uncovered part has a horizontal length of $4$.
If the window is completely covered, print $0$.
Each curtain may be longer than the window.