#include <bits/stdc++.h>
using namespace std;
int main() {
  int k, n, s, p;
  long long sol;
  cin >> k >> n >> s >> p;
  sol = (n + s - 1) / s;
  sol = sol * k;
  sol = sol + p - 1;
  sol = sol / p;
  cout << sol;
}
