#include <bits/stdc++.h>
using namespace std;
long long k, n, s, p;
int main() {
  ios_base::sync_with_stdio(false);
  cin >> k >> n >> s >> p;
  int t = ceil(k * n * 1.0 / s);
  int v = ceil(t * 1.0 / k);
  cout << (long long)ceil(v * k * 1.0 / p);
  return 0;
}
