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 n: usize = itr.next().unwrap().parse().unwrap();
    let k: usize = itr.next().unwrap().parse().unwrap();

    let mut dp1: Vec<f64> = vec![0.0; 101];
    let mut dp2: Vec<f64> = vec![0.0; 101];
    dp1[0] = 1.0;
    dp2[0] = 1.0;
    for _ in 0..n - k {
        let mut tmp = vec![0.0; 101];
        for i in 0..80 {
            for j in 1..7 {
                tmp[i + j] += dp1[i] / 6.0;
            }
        }
        dp1 = tmp;
    }
    for _ in 0..k {
        let mut tmp = vec![0.0; 101];
        for i in 0..80 {
            for j in 4..7 {
                tmp[i + j] += dp1[i] / 3.0;
            }
        }
        dp1 = tmp;
    }

    for _ in 0..n {
        let mut tmp = vec![0.0; 101];
        for i in 0..80 {
            for j in 1..7 {
                tmp[i + j] += dp2[i] / 6.0;
            }
        }
        dp2 = tmp;
    }

    let mut ans = 0.0;
    for i in 0..80 {
        for j in 0..i {
            ans += dp1[i] * dp2[j];
        }
    }
    println!("{:.10}", ans);
}