#include <bits/stdc++.h>
using namespace std;
int main() {
  int k, n, s, p, sheetsPerPerson, res;
  cin >> k >> n >> s >> p;
  if (n % s)
    sheetsPerPerson = n / s + 1;
  else
    sheetsPerPerson = n / s;
  res = k * sheetsPerPerson;
  if (res % p) {
    res /= p;
    res++;
  } else
    res /= p;
  cout << res << endl;
  return 0;
}
