#include <bits/stdc++.h>
using namespace std;
const int MOD = 1e9 + 7;
const long double PI = 3.141592653589793238462643383279502884197;
long long fac[1] = {1}, inv[1] = {1};
long long gcd(long long a, long long b) { return b ? gcd(b, a % b) : a; }
long long mp(long long a, long long b) {
  long long ret = 1;
  while (b) {
    if (b & 1) ret = ret * a % MOD;
    a = a * a % MOD;
    b >>= 1;
  }
  return ret;
}
long long cmb(long long r, long long c) {
  return (c > r || c < 0) ? 0 : fac[r] * inv[c] % MOD * inv[r - c] % MOD;
}
int main() {
  int k, n, s, p;
  scanf("%d %d %d %d", &n, &k, &s, &p);
  int kk = 0;
  if (k % s) kk++;
  k /= s;
  k += kk;
  k *= n;
  int ans = 0;
  if (k % p) ans++;
  ans += k / p;
  printf("%d", ans);
}
