#include <bits/stdc++.h>
using namespace std;

int main() {
    ios_base::sync_with_stdio(false);
    cin.tie(nullptr);

    int N; cin >> N;
    map<int,double,greater<>> P;
    double answer = 0;
    P[N] = 1;
    for(auto [i,p] : P){
        if(i == 1) break;
        vector<int> D;
        for(int k=1; k*k<=i; k++){
            if(i%k) continue;
            D.push_back(k);
            if(k*k != i) D.push_back(i/k);
        }
        sort(D.begin(),D.end());
        int n = D.size();
        vector<int> C(n);
        for(int k=n-1; k>=0; k--){
            int d = D.at(k);
            int now = N/d;
            for(int l=k+1; l<n; l++) if(D.at(l)%d == 0) now -= C.at(l);
            C.at(k) = now;
        }
        double multi = N/(0.0+N-C.at(n-1));
        answer += multi*p;
        for(int k=0; k<n-1; k++){
            int d = D.at(k);
            P[d] += p*C.at(k)/(N-C.at(n-1));
        }
    }
    cout << fixed << setprecision(20) << answer << endl;

}