#include <bits/stdc++.h>
using namespace std;
template <class T>
T abs(T x) {
  if (x < 0) return -x;
  return x;
}
template <class T>
T sqr(T a) {
  return a * a;
}
const double pi = acos(-1.0);
const double eps = 1e-8;
int main() {
  int k, n, s, p, pac, ans, a;
  while (4 == scanf("%d%d%d%d", &k, &n, &s, &p)) {
    a = n / s;
    if (n % s != 0) a++;
    a = a * k;
    ans = a / p;
    if (a % p != 0) ans++;
    printf("%d\n", ans);
    ;
  }
  return 0;
}
