A - Curtain

Time Limit: 2 sec / Memory Limit: 1024 MB

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≤A≤100
1≤B≤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.

Sample Input 1
12 4
Sample Output 1
4
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.

Sample Input 2
20 15
Sample Output 2
0
If the window is completely covered, print 0.

Sample Input 3
20 30
Sample Output 3
0
Each curtain may be longer than the window.

题目大意

窗户长度是A，窗户上有两个窗帘，每个窗帘的长度是B，问窗户最多还有多长没有被窗帘覆盖。

#include <bits/stdc++.h>
using namespace std;
int main(){
    int a, b;
    cin >> a >> b;
    if(a-2*b>0)
        cout << a-2*b;
    else
        cout << 0;
    return 0;
}