#include <bits/stdc++.h>
using namespace std;
int main() {
  int k, n, s, p;
  cin >> k >> n >> s >> p;
  int total = k * n;
  int paper = 0;
  while (true) {
    if (paper * s >= n) {
      break;
    } else
      ++paper;
  }
  paper *= k;
  int ans = 0;
  while (true) {
    if (ans * p >= paper) {
      cout << ans;
      break;
    } else
      ++ans;
  }
}
