#include <bits/stdc++.h>   using namespace std;   const int N = 1e6 + 5;   const int M = 1e9 + 7;   long long a[N];   int main() {     ios_base::sync_with_stdio(false);     cin.tie(NULL);     cout.tie(NULL);     long long d;     cin >> a[0] >> a[1] >> a[2] >> d;     sort(a, a + 3);     cout << max(0ll, a[0] - a[1] + d) + max(0ll, a[1] + d - a[2]);   }   