#include <bits/stdc++.h>
#pragma GCC optimize("O3")
constexpr auto INF = 9223372036854775807;
using namespace std;
struct custom_hash {
  static uint64_t splitmix64(uint64_t x) {
    x += 0x9e3779b97f4a7c15;
    x = (x ^ (x >> 30)) * 0xbf58476d1ce4e5b9;
    x = (x ^ (x >> 27)) * 0x94d049bb133111eb;
    return x ^ (x >> 31);
  }
  size_t operator()(uint64_t x) const {
    static const uint64_t FIXED_RANDOM =
        chrono::steady_clock::now().time_since_epoch().count();
    return splitmix64(x + FIXED_RANDOM);
  }
};
inline int mex(unordered_set<int> st) {
  int m = 0;
  while (st.find(m) != st.end()) {
    m += 1;
  }
  return m;
}
inline int calculateGrundy(int n) {
  if (n == 1) return 0;
  unordered_set<int> mexi;
  for (int i = 1; i <= sqrt(n); i += 1) {
    if (n % i == 0) {
      if (n / i != n) mexi.insert(calculateGrundy(n / i));
      mexi.insert(calculateGrundy(i));
    }
  }
  return mex(mexi);
}
inline long long int gcd(long long int a, long long int b) {
  if (b == 0) return a;
  return gcd(b, a % b);
}
long long int power(long long int x, long long int y) {
  long long int res = 1;
  x = x;
  while (y > 0) {
    if (y & 1) res = (res * x);
    y = y >> 1;
    x = (x * x);
  }
  return res;
}
long long int sum(long long int n) { return (n * (n + 1)) / 2; }
long long int sum_digit(long long int n) {
  long long int ans = 0;
  while (n) {
    ans += n % 10;
    n /= 10;
  }
  return ans;
}
int main() {
  ios_base::sync_with_stdio(0), cin.tie(0), cout.tie(0);
  long long int k, n, s, p;
  cin >> k >> n >> s >> p;
  long long int pages = (n) / s;
  if (n % s != 0) pages += 1;
  long long int ans = (k * pages) / p;
  if ((k * pages) % p != 0) {
    ans += 1;
  }
  cout << ans;
  return 0;
}
