#include <bits/stdc++.h>
using namespace std;
int main() {
  int ans, n, k, s, p;
  scanf("%d%d%d%d", &k, &n, &s, &p);
  ans = (((n - 1) / s + 1) * k - 1) / p + 1;
  printf("%d\n", ans);
  return 0;
}
