#include <bits/stdc++.h>
using namespace std;
bool checker(int N) {
  if (N != 0) return 1;
  return 0;
}
int main() {
  int n, s, k, p;
  cin >> k >> n >> s >> p;
  int sheets = n / s + checker(n % s);
  int ans = (k * (sheets)) / p + checker((k * sheets) % p);
  cout << ans;
}
