#include <bits/stdc++.h>
using namespace std;
const int N = 1e6 + 5;
const long long int inf = -1e18;
const int MOD = 1e9 + 7;
int main() {
  ios_base::sync_with_stdio(0);
  cin.tie(NULL);
  cout.tie(NULL);
  long long int k, n, s, p, mk, out;
  cin >> k >> n >> s >> p;
  mk = n / s;
  if (n % s) mk++;
  mk = k * mk;
  out = mk / p;
  if (mk % p) out++;
  cout << out;
  return 0;
}
