import java.io.*;
import java.util.*;

public class Main {
    static HashSet<String> ans = new HashSet<>();
    public static void main(String[] args) throws Exception {
        Scanner sc = new Scanner();
        int n = sc.nextInt();
        int k = sc.nextInt();
        int[][] taro = new int[n + 1][n * 6 + 1];
        int[][] jiro = new int[n + 1][n * 6 + 1];
        taro[0][0] = 1;
        jiro[0][0] = 1;
        for (int i = 1; i <= n; i++) {
            for (int j = (i - 1) * 1; j <= (i - 1) * 6; j++) {
                for (int a = 1; a <= 6; a++) {
                    jiro[i][j + a] += jiro[i - 1][j];
                }
                if (i <= k) {
                    for (int a = 4; a <= 6; a++) {
                        taro[i][j + a] += taro[i - 1][j] * 2;
                    }
                } else {
                    for (int a = 1; a <= 6; a++) {
                        taro[i][j + a] += taro[i - 1][j];
                    }
                }
            }
        }
        double sum = 0;
        double ans = 0;
        for (int i = 0; i <= n * 6; i++) {
            ans += sum * taro[n][i];
            sum += jiro[n][i];
        }
        ans /= Math.pow(Math.pow(6, n), 2);
        System.out.println(new java.math.BigDecimal(ans).toPlainString());
    }
}
class Scanner {
    BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
    StringTokenizer st = new StringTokenizer("");
    
    public Scanner() throws Exception {
        
    }
    
    public int nextInt() throws Exception {
        return Integer.parseInt(next());
    }
    
    public long nextLong() throws Exception {
        return Long.parseLong(next());
    }
    
    public double nextDouble() throws Exception {
        return Double.parseDouble(next());
    }
    
    public String next() throws Exception {
        while (!st.hasMoreTokens()) {
            st = new StringTokenizer(br.readLine());
        }
        return st.nextToken();
    }
}