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