#include<bits/stdc++.h>
namespace {
#pragma GCC diagnostic ignored "-Wunused-function"
#include<atcoder/all>
#pragma GCC diagnostic warning "-Wunused-function"
using namespace std;
using namespace atcoder;
#define rep(i,n) for(int i = 0; i < (int)(n); i++)
#define rrep(i,n) for(int i = (int)(n) - 1; i >= 0; i--)
#define all(x) begin(x), end(x)
#define rall(x) rbegin(x), rend(x)
template<class T> bool chmax(T& a, const T& b) { if (a < b) { a = b; return true; } else return false; }
template<class T> bool chmin(T& a, const T& b) { if (b < a) { a = b; return true; } else return false; }
using ll = long long;
using P = pair<int,int>;
using VI = vector<int>;
using VVI = vector<VI>;
using VL = vector<ll>;
using VVL = vector<VL>;

double solve() {
  int n;
  cin >> n;
  if (n == 0) return 0.4;
  if (n == 1) return 1.111447;
  if (n == 2) return 2.871864;
  const double n3 = n * n * n;
  double ans = 0;
  constexpr int B = 100000;
  rep(s, B) {
    double x = s / (double)B;
    ans += sqrt(x * x * x + n3);
  }
  return ans / B;
}

} int main() {
  ios::sync_with_stdio(false);
  cin.tie(0);
  cout << fixed << setprecision(5) << solve() << endl;
}