#include <bits/stdc++.h>
using namespace std;
int main() {
  long long k, n, s, p, each_sheet, temp;
  cin >> k >> n >> s >> p;
  if (n % s == 0)
    each_sheet = n / s;
  else
    each_sheet = n / s + 1;
  long long total = each_sheet * k;
  if (total % p == 0)
    cout << total / p;
  else
    cout << total / p + 1;
  return 0;
}
