#include <bits/stdc++.h>
using namespace std;
const int N = 1e5 + 10;
int main() {
  ios_base::sync_with_stdio(0);
  cin.tie(0);
  cout.tie(0);
  long long n, k, s, p, nums = 1, nump = 1;
  cin >> k >> n >> s >> p;
  while (nums * s < n) nums++;
  while (p * nump < nums * k) nump++;
  cout << nump << endl;
  return 0;
}
