#include <bits/stdc++.h>
using namespace std;
int main() {
  int i, j, k, n, m, s, p, st;
  cin >> k >> n >> s >> p;
  int cnt = n / s;
  if (n % s != 0) cnt++;
  cnt = cnt * k;
  int tot = cnt / p;
  if (cnt % p != 0) tot++;
  cout << tot;
}
