#include <bits/stdc++.h>
using namespace std;
int main() {
  int k, n, s, p;
  cin >> k >> n >> s >> p;
  int ans = (n / s);
  if (n % s) ans++;
  ans *= k;
  int kk = ans / p;
  if (ans % p) kk++;
  cout << kk << endl;
}
