#include <bits/stdc++.h>
using namespace std;
const int maxn = 5e4 + 5;
int main() {
  int k, n, s, p;
  cin >> k >> n >> s >> p;
  int ans = k * (n % s == 0 ? n / s : n / s + 1);
  if (ans % p == 0)
    cout << ans / p << endl;
  else
    cout << ans / p + 1 << endl;
  return 0;
}
