#include <bits/stdc++.h>
using namespace std;
const long long int LL_MAX = 1e18 + 5;
const int MX = INT_MAX;
const long long int mod = 1000000007;
const int maxx = 2e5;
const int d4i[4] = {-1, 0, 1, 0};
const int d4j[4] = {0, 1, 0, -1};
const int d8i[8] = {-1, -1, 0, 1, 1, 1, 0, -1};
const int d8j[8] = {0, 1, 1, 1, 0, -1, -1, -1};
bool rev(int a, int b) { return a >= b; }
string yy = "YES", no = "NO";
void solve() {
  int k, n, s, p;
  cin >> k >> n >> s >> p;
  ;
  int ans = ((k * ((n + s - 1) / s) + p - 1)) / p;
  cout << ans << "\n";
}
int main() {
  ios_base::sync_with_stdio(false);
  cin.tie(NULL);
  cout.tie(NULL);
  solve();
  return 0;
}
