fn main() {
    let mut k = String::new();
    std::io::stdin().read_line(&mut k).ok();
    let k: usize = k.trim().parse().unwrap();

    let mut p = vec![0.; k + 1];
    for i in (0..k).rev() {
        p[i] = p.iter().skip(i + 1).take(6).map(|x| x / 6.).sum::<f64>() + 1.;
    }

    println!("{}", p[0]);
}