#include <bits/stdc++.h>
using namespace std;
using ll = long long;
#define all(A) A.begin(),A.end()
using vll = vector<ll>;
#define rep(i, n) for (long long i = 0; i < (long long)(n); i++)
using Graph = vector<vector<ll>>;
ll mod=998244353;
ll inva(ll N) {
    ll a = N, b = mod, c = 1, d = 0;
    while (b > 0) {
        ll t = a / b;
        a -= t * b;
        swap(a, b);
        c -= t * d;
        swap(c, d);

    }
    c %= mod;
    if (c < 0)c += mod;
    return c;

}//割り算時に使う逆元を求める.


int main() {
    ll N;
    cin>>N;
    double an=1.0;
    for(ll i=2;i<=N;i++){
        an+=2.0/double(i);
        if(i==2)continue;
        double k=i*(3*i-1)/12.0;
        
        an+=(double(i)-2.0)/double(i)*k;
    }
    cout<<setprecision(16)<<an<<endl;
}