#include <bits/stdc++.h>
using namespace std;
int main() {
  long long k, n, s, p;
  cin >> k >> n >> s >> p;
  long long sht = (n / s) + (n % s > 0);
  sht *= k;
  cout << sht / p + (sht % p > 0);
  return 0;
}
