#include <bits/stdc++.h>

using namespace std;

typedef long long int64;

int main()
{
  int M, P, D, S;
  cin >> P >> D >> M >> S;

  int64 ret = 0;
  while(S - P >= 0) {
    S -= P;
    P -= D;
    P = max(P, M);
    ++ret;
  }

  cout << ret << endl;
}