#include <bits/stdc++.h>
using namespace std;
int main() {
  int k = 0, n = 0, s = 0, p = 0;
  cin >> k >> n >> s >> p;
  int npgpp = 0;
  npgpp = ceil(float(n) / float(s));
  int npgt = 0;
  npgt = npgpp * k;
  int np = 0;
  np = ceil(float(npgt) / float(p));
  cout << np << endl;
}
