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