#include <bits/stdc++.h>
using namespace std;
int main() {
  int k, n, s, p, sheet = 0, tot = 0, result = 0;
  cin >> k >> n >> s >> p;
  while (n >= s) {
    sheet += 1;
    n = n - s;
  }
  if (n != 0 && n < s) {
    sheet += 1;
  }
  tot = sheet * k;
  if (tot % p == 0) {
    result = tot / p;
  } else {
    while (tot % p != 0) {
      tot += 1;
    }
    result = tot / p;
  }
  cout << result;
}
