#include <bits/stdc++.h>
using namespace std;
void solve() {
  long long n, k, s, p;
  cin >> k >> n >> s >> p;
  cout << (((n + s - 1) / s) * k + p - 1) / p;
}
int main() {
  int q = 1;
  while (q--) {
    solve();
    cout << endl;
  }
}
