#include <bits/stdc++.h>
using namespace std;
int main() {
  long long k, n, s, p;
  scanf("%lld %lld %lld %lld", &k, &n, &s, &p);
  long long j = (n / s);
  if (n % s != 0) j++;
  j *= k;
  long long x = j / p;
  if (j % p != 0) x++;
  printf("%lld\n", x);
  return 0;
}
