#![allow(non_snake_case)]
#[allow(unused_imports)]
use proconio::{fastout, input, marker::*};

#[fastout]
fn main() {
    input! {
        N: usize,
    }

    let mut sieve = vec![vec![]; 10_000_010];

    for p in 2u32..=10_000_000 {
        if sieve[p as usize].is_empty() {
            for q in (p * 2..10_000_010).step_by(p as usize) {
                sieve[q as usize].push(p);
            }
        }
    }

    let mut dp = vec![0.; 10_000_010];

    for k in 2..=10_000_000 {
        let mut s = 0.;
        let mut cnt = 0;

        for &d in sieve[k].iter() {
            if sieve[k].len() == 1 {
                s += dp[d as usize];
                cnt += 1;
            } else if d == sieve[k][0] {
                let m = sieve[k][1];

                s += dp[d as usize] * (m - 1) as f32;
                cnt += m - 1;
            } else {
                let m = sieve[k][0];

                s += dp[d as usize] * (m - 1) as f32;
                cnt += m - 1;
            }
        }

        dp[k] = s + (1 * (k - 1 - cnt as usize)) as f32;
        dp[k] /= (k - 1) as f32;
        dp[k] += (k) as f32 / (k - 1) as f32;
    }

    println!("{}", dp[N] - 1.);
}