fn main() {
    input!(n: usize);
    let mut ans = 0f64;
    /*
    for i in 1..=n {
        for j in 1..=(n / i) {
            ans += 1.0 / (i * j) as f64;
        }
    }
    */
    let m = 1000000;
    let mut memo = vec![0f64; m + 1];
    for i in 1..memo.len() {
        memo[i] = memo[i - 1] + 1.0 / i as f64;
    }
    let eval = |n: usize| -> f64 {
        if let Some(v) = memo.get(n) {
            *v
        } else {
            (n as f64).ln() + 0.57721566490153286060
        }
    };
    quot_range_unorderd(n, |l, r, q| {
        let x = eval(r) - eval(l - 1);
        let y = eval(q);
        ans += x * y;
    });
    println!("{:.7}", ans);
}

// ---------- begin quot_range ----------
#[allow(dead_code)]
pub fn quot_range_unorderd<F>(n: usize, mut f: F)
where
    F: FnMut(usize, usize, usize)
{
    let mut pre = (0, 0);
    for d in 1.. {
        let q = n / d;
        if pre != (0, 0) {
            let (q, l, r) = (pre.0, q + 1, pre.1);
            f(l, r, q);
        }
        if q < d {
            break;
        }
        pre = (d, q);
        f(d, d, q);
        if q == d {
            break;
        }
    }
}
// ---------- begin quot_range ----------
// ---------- begin input macro ----------
// reference: https://qiita.com/tanakh/items/0ba42c7ca36cd29d0ac8
#[macro_export]
macro_rules! input {
    (source = $s:expr, $($r:tt)*) => {
        let mut iter = $s.split_whitespace();
        input_inner!{iter, $($r)*}
    };
    ($($r:tt)*) => {
        let s = {
            use std::io::Read;
            let mut s = String::new();
            std::io::stdin().read_to_string(&mut s).unwrap();
            s
        };
        let mut iter = s.split_whitespace();
        input_inner!{iter, $($r)*}
    };
}

#[macro_export]
macro_rules! input_inner {
    ($iter:expr) => {};
    ($iter:expr, ) => {};
    ($iter:expr, $var:ident : $t:tt $($r:tt)*) => {
        let $var = read_value!($iter, $t);
        input_inner!{$iter $($r)*}
    };
}

#[macro_export]
macro_rules! read_value {
    ($iter:expr, ( $($t:tt),* )) => {
        ( $(read_value!($iter, $t)),* )
    };
    ($iter:expr, [ $t:tt ; $len:expr ]) => {
        (0..$len).map(|_| read_value!($iter, $t)).collect::<Vec<_>>()
    };
    ($iter:expr, chars) => {
        read_value!($iter, String).chars().collect::<Vec<char>>()
    };
    ($iter:expr, bytes) => {
        read_value!($iter, String).bytes().collect::<Vec<u8>>()
    };
    ($iter:expr, usize1) => {
        read_value!($iter, usize) - 1
    };
    ($iter:expr, $t:ty) => {
        $iter.next().unwrap().parse::<$t>().expect("Parse error")
    };
}
// ---------- end input macro ----------