#include <bits/stdc++.h>
int main() {
  int paperlist, people, planes, plan, i, j, k, listatpeople, needpaper, ans;
  scanf("%d %d %d %d", &people, &planes, &plan, &paperlist);
  listatpeople = planes / plan;
  if (planes % plan != 0) listatpeople++;
  needpaper = people * listatpeople;
  ans = needpaper / paperlist;
  if (needpaper % paperlist != 0) {
    ans++;
  }
  printf("%d", ans);
  getchar();
  getchar();
  return 0;
}
