use std::io::*;

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: usize = itr.next().unwrap().parse().unwrap();

    // dp[i<0] = dp[k], ループするのでこれを固定する
    let mut dp: Vec<f64> = vec![0.0; k + 5];
    let mut l = 0.0;
    let mut r = 1000.0;

    for _ in 0..1000 {
        let mid = (l + r) / 2.0;
        dp[0] = 0.0;
        for i in 1..k + 1 {
            dp[i] = 1.0;
            for j in 1..7 {
                if i < j {
                    dp[i] += mid / 6.0;
                } else {
                    dp[i] += dp[i - j] / 6.0;
                }
            }
        }
        if dp[k] > mid {
            l = mid;
        } else {
            r = mid;
        }
    }
    println!("{:.10}", dp[k]);
}