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