#include <bits/stdc++.h>
using namespace std;
int main() {
  int k, n, s, p, b, c;
  cin >> k >> n >> s >> p;
  float a = (n * 1.0) / s;
  b = ceil(a);
  c = b * k;
  float d = (c * 1.0) / p;
  int t = ceil(d);
  cout << t;
}
