codeforce - ropewalker

#include<bits/stdc++.h>
using namespace std;
int main()
{
    long long ara[3],d,ans=0;
    cin>>ara[0]>>ara[1]>>ara[2]>>d;
    sort(ara,ara+3);
    if(ara[1]-ara[0]<d)ans+=d-(ara[1]-ara[0]);
    if(ara[2]-ara[1]<d)ans+=d-(ara[2]-ara[1]);
    cout<<ans<<endl;
}