#include <bits/stdc++.h>
int main() {
  int k, n, s, p, t, j;
  scanf("%d%d%d%d", &k, &n, &s, &p);
  if (n % s == 0)
    t = n / s;
  else
    t = n / s + 1;
  j = t * k;
  if (j % p == 0)
    printf("%d", j / p);
  else
    printf("%d", j / p + 1);
}
