#include <bits/stdc++.h>
using namespace std;
int div1(int a, int b) {
  if (a % b == 0)
    return a / b;
  else
    return a / b + 1;
}
int main() {
  int k, n, s, p;
  while (scanf("%d%d%d%d", &k, &n, &s, &p) != EOF) {
    int ever_need = div1(n, s);
    int ans = div1(ever_need * k, p);
    printf("%d\n", ans);
  }
  return 0;
}
