#include <bits/stdc++.h>
using namespace std;
int main() {
  long long k, n, s, p;
  cin >> k >> n >> s >> p;
  long long int sh = ceil(n / (1.0 * s));
  long long int tot = sh * k;
  long long int ans = ceil(tot / (1.0 * p));
  cout << ans << endl;
}
