#include <bits/stdc++.h>
using namespace std;
long long k, n, s, p;
signed main() {
  ios_base::sync_with_stdio(false);
  cin.tie(0);
  cin >> k >> n >> s >> p;
  long long res = (n + s - 1) / s;
  res *= k;
  res = (res + p - 1) / p;
  cout << res;
}
