#include <bits/stdc++.h>
using namespace std;
using lint = long long;
using pii = pair<int, int>;
using pll = pair<lint, lint>;
template <typename T>
using vc = vector<T>;
template <typename T>
using vvc = vector<vector<T>>;
template <typename T>
inline bool chmax(T& a, T b) {
  if (a < b) {
    a = b;
    return true;
  }
  return false;
}
template <typename T>
inline bool chmin(T& a, T b) {
  if (a > b) {
    a = b;
    return true;
  }
  return false;
}
constexpr lint ten(int n) { return n == 0 ? 1 : ten(n - 1) * 10; }
class Task {
 public:
  void solve(istream& in, ostream& out) {
    int k, n, s, p;
    in >> k >> n >> s >> p;
    int t = (n + s - 1) / s * k;
    out << (t + p - 1) / p << '\n';
  }
};
int main() {
  istream& in(cin);
  ostream& out(cout);
  ios_base::sync_with_stdio(false);
  in.tie(nullptr), out.tie(nullptr);
  Task solver;
  solver.solve(in, out);
  return 0;
}
