#include <bits/stdc++.h>
const int inf = INT_MAX;
const int mod = 1e9 + 7;
const int maxn = 1e5 + 111;
using namespace std;
int main() {
  int k, n, second, p;
  cin >> k >> n >> second >> p;
  int x = n / second;
  if (n % second != 0) x++;
  int cnt = 1;
  while (cnt * p < k * x) cnt++;
  cout << cnt;
}
