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