#include <bits/stdc++.h>
using namespace std;
int main() {
  int k, n, s, p;
  cin >> k >> n >> s >> p;
  int g = n / s;
  if (n % s) g++;
  int ss = g * k / p;
  if ((g * k) % p) ss++;
  cout << ss << endl;
  return 0;
}
