#include <bits/stdc++.h>
using namespace std;
int main() {
  long long int k, st, n, s, p, nos;
  cin >> k >> n >> s >> p;
  if (n % s)
    nos = (n / s) + 1;
  else
    nos = (n / s);
  st = nos * k;
  if (st % p)
    cout << (st / p) + 1;
  else
    cout << (st / p);
}
