use std::io::*;

fn e(x: i32, k: i32) -> f64 {
    if x >= k {
        0.0
    } else {
        e(x + 1, k) / 6.0
            + e(x + 2, k) / 6.0
            + e(x + 3, k) / 6.0
            + e(x + 4, k) / 6.0
            + e(x + 5, k) / 6.0
            + e(x + 6, k) / 6.0
            + 1.0
    }
}

fn main() {
    let mut s: String = String::new();
    std::io::stdin().read_to_string(&mut s).ok();
    let mut itr = s.trim().split_whitespace();
    let k: i32 = itr.next().unwrap().parse().unwrap();
    println!("{:.10}", e(0, k));
}