#include <bits/stdc++.h>
using namespace std;
int r, j, l, x, y, m, c, n, s, f, q, i, z, p, k, d, t, u, e, g, val, no;
string s1, s2, s3, s4;
int main() {
  ios_base::sync_with_stdio(false);
  cin.tie(NULL);
  cout.tie(NULL);
  cin >> k >> n >> s >> p;
  l = n / s;
  y = (l * s);
  if (y != n) {
    l++;
  }
  l = l * k;
  y = (l / p);
  z = y * p;
  if (z != l) {
    y++;
  }
  cout << y;
}
