#include <bits/stdc++.h>
#pragma GCC optimize("O3")
using namespace std;
const int N = 100 + 5;
int main() {
  long long k, n, s, p;
  cin >> k >> n >> s >> p;
  long long marda = n / s;
  if (n % s != 0) marda++;
  long long sax = k * marda;
  long long ans = sax / p;
  if (sax % p != 0) ans++;
  cout << ans << endl;
  return 0;
}
