use std::cmp::min;

fn main() {
    let mut k = String::new();
    std::io::stdin().read_line(&mut k).ok();
    let k: usize = k.trim().parse().unwrap();
    
    let mut result: Vec<usize> = vec![0; k+1];
    result[0] = 1;
    let mut e: f64 = 0.0;
    for i in 1..=k {
        for j in (0..k).rev() {
            if result[j] == 0 { continue; }
            for d in 1..=6 {
                let count = result[j];
                let nextval = min(k, j + d);
                result[nextval] += count;
            }
            result[j] = 0;
        }
        e += (i  * result[k]) as f64 / (6usize.pow(i as u32) as f64);
        result[k] = 0;
    }
    println!("{:.4}", e);
}