#include <bits/stdc++.h>
const long long LINF = 1e18;
const int INF = 1e9;
const int M = 1e9 + 7;
const double EPS = 1e-9;
using namespace std;
int main(int argc, const char* argv[]) {
  std::ios_base::sync_with_stdio(0);
  long double k, n, s, p;
  cin >> k >> n >> s >> p;
  long long numforone = ceil((double)n / s);
  long long ans = ceil((double)(k * numforone) / p);
  cout << ans;
  return 0;
}
