#include <bits/stdc++.h>
using namespace std;
const long long inf = (long long)1e18;
long long gcd(long long a, long long b) {
  long long r;
  while (b) {
    r = a % b;
    a = b;
    b = r;
  }
  return a;
}
long long lcm(long long a, long long b) { return a / gcd(a, b) * b; }
long long fpow(long long n, long long k, int p = 1000000007) {
  long long r = 1;
  for (; k; k >>= 1) {
    if (k & 1) r = r * n % p;
    n = n * n % p;
  }
  return r;
}
int inv(int a, int p = 1000000007) { return fpow(a, p - 2, p); }
long long spf[1000001 + 1];
void sieve() {
  for (int i = 1; i < 1000001; i++) {
    spf[i] = i;
  }
  for (long long i = 2; i < 1000001; i += 2) {
    spf[i] = 2;
  }
  for (long long i = 3; i < 1000001; i += 2) {
    if (spf[i] == i) {
      for (long long j = i * i; j < 1000001; j += i) {
        spf[j] = min(i, (long long)spf[j]);
      }
    }
  }
}
int main() {
  double k, n, s, p;
  cin >> k >> n >> s >> p;
  double oneperson = ceil(n / s);
  double mulperson = (oneperson * k);
  long long packs = ceil(mulperson / p);
  cout << packs << endl;
}
