#include <bits/stdc++.h>
using namespace std;
int k, n, s, p, num, t;
int main() {
  ios::sync_with_stdio(false);
  cin.tie(0);
  cout.tie(0);
  cin >> k >> n >> s >> p;
  num = n / s;
  if (n % s) ++num;
  if (n <= s) num = 1;
  t = (num * k / p);
  if (num * k % p) ++t;
  if (num * k <= p) t = 1;
  cout << t << endl;
  return 0;
}
