#include <bits/stdc++.h>
using namespace std;
int main() {
  int k, n, s, p;
  cin >> k >> n >> s >> p;
  int sheets_per_person = (n + s - 1) / s;
  int total_sheets = sheets_per_person * k;
  int packs = (total_sheets + p - 1) / p;
  cout << packs << endl;
  return 0;
}
