#include <bits/stdc++.h>
using namespace std;
int main() {
  long long n, a, b, c;
  cin >> n >> a >> b >> c;
  long long temp;
  if (a % b == 0)
    temp = a / b;
  else
    temp = a / b + 1;
  long long te = n * temp;
  if (te % c == 0)
    cout << te / c;
  else
    cout << te / c + 1;
  return 0;
}
