#include <bits/stdc++.h>
using namespace std;
int main() {
  ios::sync_with_stdio(false);
  cin.tie(0);
  int k, n, s, p;
  cin >> k >> n >> s >> p;
  int sheets_per_person = (n + s - 1) / s;
  int total_sheets_needed = k * sheets_per_person;
  cout << (total_sheets_needed + p - 1) / p << '\n';
  return 0;
}
