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