#include <bits/stdc++.h>
using namespace std;
int main() {
  int k, b, n, t;
  cin >> k;
  cin >> b;
  cin >> n;
  cin >> t;
  int querty_eq_exp_2 = (k * t) + b;
  int z = n * (k + b);
  if (z <= t)
    cout << 0 << endl;
  else {
    cout << float(z / querty_eq_exp_2) + 1 << endl;
  }
  return 0;
}
