import java.util.Arrays;
import java.util.Scanner;

public class Main58 {
	public static void main(String[] args) {
		Main58 p = new Main58();
	}

	public Main58() {
		Scanner sc = new Scanner(System.in);
		int n = sc.nextInt();
		int k = sc.nextInt();
		
		solve(n, k);
	}

	public void solve(int n, int K) {
		int[][] tdp = new int[n+1][n*6+1];
		int[][] jdp = new int[n+1][n*6+1];
		tdp[0][0] = 1;
		jdp[0][0] = 1;
		for(int i=0;i<n;i++){
			for(int j=0;j<6;j++){
				int s = tdp[i].length - 1 - (i<K ? (j/2+4) : (j+1));
				for(int k=s;k>=0;k--){
					if(i<K)
						tdp[i+1][j/2+4+k] += tdp[i][k];
					else
						tdp[i+1][j+1+k] += tdp[i][k];
				}
				
				for(int k=s;k>=0;k--)
					jdp[i+1][j+1+k] += jdp[i][k];

			}
		}
		
//		System.out.println(Arrays.toString(tdp[n]));
//		System.out.println(Arrays.toString(jdp[n]));
		
		long jsum = 0;
		long count = 0;
		
		for(int i=1;i<tdp[n].length;i++){
			jsum += jdp[n][i-1];
			if(tdp[n][i] == 0)
				continue;
			
			count += tdp[n][i]*jsum;		
		}
		
		long total = 1;
		for(int i=0;i<n;i++)
			total *= 6;
		
		System.out.println((double)count/(total*total));
		
	}

}