#include <bits/stdc++.h>
#include <atcoder/all>
using ll = long long;
#define MOD 1000000007
#define Mod 998244353
const int MAX = 1000000005;
const long long INF = 1000000000000000005LL;
using namespace std;
using namespace atcoder;

map<int, long double> dp;
long double rec(int n) {
    if (dp.count(n)) return dp[n];
    if (n == 1) return 0;
    long double s = 0;
    for (int m = 2; m*m <= n; m++) {
        if (n % m == 0) s += rec(m);
    }
    return dp[n] = (long double)n/(n - 1) + s/(n - 1);
}

int main() {
    ios::sync_with_stdio(0);cin.tie();
    int N;
    cin >> N;
    cout << fixed << setprecision(12) << rec(N) << endl;
}