use proconio::input;
use std::io::{stdout,Write,BufWriter};

fn e(x:usize, k:usize) -> f32 {
    if x>=k {return 0.0}
    return  (e(x+1, k) + e(x+2, k) + e(x+3, k) + e(x+4, k) + e(x+5, k) + e(x+6, k)) / 6.0 + 1.0
}

fn main() {
    input!{
        k:usize
    }

    let out = stdout();
    let mut out = BufWriter::new(out.lock());
    
    write!(out, "{}", e(0, k)).unwrap();
}