#include <bits/stdc++.h>
using namespace std;
int main() {
  double k, n, s, p, a = 0, b = 0, c = 0;
  int d = 0;
  cin >> k >> n >> s >> p;
  a = (n / s);
  b = ceil(a) * k;
  c = b / p;
  d = ceil(c);
  cout << d << endl;
  return 0;
}
