#include <bits/stdc++.h>
using namespace std;
using ll = long long;
#define rep(i, n) for (int i = 0; i < (int)(n); i++)

double f(double a, ll n) {
  double res = 1;
  rep(i, n) res *= a + i;
  return res;
}

void solve() {
  ll n;
  cin >> n;
  if (n == 0) {
    cout << "0.4\n";
    return;
  }
  double ans = 0, c = 1, d = 1;
  rep(i, 50) {
    double now = 1;
    now *= f(-1.0 / 2.0, i);
    now *= f(1.0 / 3.0, i);
    now /= f(4.0 / 3.0, i);
    now *= c;
    now /= d;
    c *= -1.0 / double(n * n * n);
    d *= i + 1;
    ans += now;
  }
  ans *= n;
  ans *= sqrt(double(n));
  cout << fixed << setprecision(6) << ans << '\n';
}

int main() {
  std::cin.tie(nullptr);
  std::ios_base::sync_with_stdio(false);
  int T = 1;
  for (int t = 0; t < T; t++) {
    solve();
  }
  return 0;
}