Competitions

# Dino and colors

Dino accidentally painted a red strip of length a on the wall of the school with red paint. Until the end of the break, it must be hidden, because if the teacher sees, then he will be very angry. Dino remembered that he had two white paints with which he can draw white stripes of length b. He wants to use these paints to hide completely the red strip with white, or to paint so that the length of the red strip on the wall will be as small as possible. Help Dino to do this.

#### Input

Two integers a and b (1a, b109).

#### Output

Print the possible minimum length of the remaining red strip.

Time limit 1 second
Memory limit 128 MiB
Input example #1
10 5
Output example #1
0
Input example #2
6 2
Output example #2
2