#include <bits/stdc++.h>
using namespace std;
int main() {
  long k, n, s, p, t1, t2;
  cin >> k >> n >> s >> p;
  t1 = n % s == 0 ? n / s : (n / s) + 1;
  t2 = (k * t1) % p == 0 ? (k * t1) / p : (k * t1) / p + 1;
  cout << t2 << endl;
  return 0;
}
