Problem:
Score : 100 points

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.

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.

Solution in C++14 (GCC 5.4.1) (judge verdict: Runtime Error)

/*
If you want to shine like a sun, first burn like a sun.
*/

#include <bits/stdc++.h>
// #include <ext/pb_ds/assoc_container.hpp> 
// #include <ext/pb_ds/tree_policy.hpp> 
// using namespace __gnu_pbds;
using namespace std;
#define mod 1000000007
#define pb push_back
#define mp make_pair
#define ll long long int
#define ld long double
#define vi vector<int>
#define vl vector<ll>
#define v2i vector<vector<int>>
#define v2l vector<vector<ll>>
#define ppi pair<int,int>
#define vpi vector<ppi>
#define ppl pair<ll,ll>
#define all(x) x.begin(),x.end()
#define ii int,int 
#define ff first    
#define ss second
#define forn(i,a,b) for(int i=a;i<b;i++)
#define forr(i,a,b) for(int i=a;i>=b;i--)
#define forv(i,m) for(auto i : m)
#define imx INT_MAX
#define imn INT_MIN
#define inf LONG_MAX
#define minf LONG_MIN
#define endl "\n"
#define fast ios_base::sync_with_stdio(false);cin.tie(NULL);
#define sze size()
#define rvs reverse 
#define itr iterator 
#define pre cout<<fixed<<setprecision(10);
#define umap unordered_map
#define uset unordered_set
#define pi 3.141592653589793
const ll infinity = 9e18;

/*
#define oset tree<int, null_type,less<int>, rb_tree_tag,tree_order_statistics_node_update>
#define MODM(a,b,md) ((a%md)*(b%md))%md
#define MODA(a,b,md) ((a%md)+(b%md))%md
#define ull unsigned long long int
*/

/*
bool compare(int a,int b) {return a > b;}
bool compare1(ppi a,ppi b) {return a.ff > b.ff;}
bool compare2(ppi a,ppi b) {return a.ss < b.ss;}
ll Npower(ll a,ll b) {ll product = 1; while(b){if(b&1){product = product*a;}a = a*a;b = b>>1;} return product;}
ll power(ll a,ll b,ll md) {ll product = 1; while(b){if(b&1){product = MODM(product,a,md);}a = MODM(a,a,md);b = b>>1;} return product%md;}
bool isprime(ll n){if(n < 2) return 0; ll i = 2; while(i*i <= n){if(n%i == 0) return 0; i++;} return 1;}
ll GCD(ll a,ll b) {return b==0 ? a:GCD(b,a%b);}
ll LCM(ll a,ll b) {return (a/GCD(a,b))*b; }
*/

int main()
{
    fast

///*
    #ifndef ONLINE_JUDGE
        freopen("in.txt",  "r",  stdin);
        freopen("out.txt", "w", stdout);
    #endif
//*/

        

        
    int a,b;
    cin>>a>>b;


    if(a > 2*b)
    {
        cout<<(a-2*b);
    }
    else
    {
        cout<<0;
    }











    return 0;
}