#include<bits/stdc++.h>
using namespace std;

int main()
{
    long long int p,d,m,s;
    cin >> p >> d >> m >> s;

    long long int count = 0,sum = 0;
    while(sum <= s)
    {
          sum += p;
          if((p-d) > m) p -= d;
          else p = m;
          count++;
    }
    cout << count-1 << endl;
    return 0;
}