#include <bits/stdc++.h>
using namespace std;
int main() {
  int k, n, s, p;
  cin >> k >> n >> s >> p;
  int shit_perperson = ceil((n / double(s)));
  int total_shit = k * shit_perperson;
  int min_packs = ceil((total_shit / double(p)));
  cout << min_packs << endl;
}
