#include <bits/stdc++.h>
using namespace std;
int main() {
  int k, n, s, pack, sheet, perPerson, p;
  cin >> k >> n >> s >> p;
  sheet = n / s;
  if (n % s > 0) sheet++;
  perPerson = (sheet * k);
  pack = perPerson / p;
  if (perPerson % p > 0) pack++;
  cout << pack;
}
