#include <iostream>
#include <vector>
#include <string>
#include <cstring>
#include <math.h>
#include <cmath>
#include <limits.h>
#include <map>
#include <set>
#include <queue>
#include <algorithm>
#include <functional>
#include <stdio.h>
#include <random>
using namespace std;

long long MOD = 1000000007;



int main() {
    
    int N,K;
    cin >> N >> K;
    
    
    long long dp1[6*N+1];
    long long dp2[6*N+1];
    
    dp1[0] = 1;
    dp2[0] = 1;
    for ( int i = 1; i < 6*N+1; i++ ) {
        dp1[i] = -1;
        dp2[i] = -1;
    }
    
    for ( int i = 0; i < N; i++ ) {
    for ( int j = 6*N; j >= 0; j-- ) {
        if ( dp1[j] != -1 ) {
            for ( int k = 1; k <= 6; k++ ) {
                if ( dp1[j+k] == -1 ) { dp1[j+k] = dp1[j]; }
                else { dp1[j+k] += dp1[j]; }                
            }
            dp1[j] = -1;
        }
    }
    }
    
    for ( int i = 0; i < N-K; i++ ) {
    for ( int j = 6*(N-K); j >= 0; j-- ) {
        if ( dp2[j] != -1 ) {
            for ( int k = 1; k <= 6; k++ ) {
                if ( dp2[j+k] == -1 ) { dp2[j+k] = dp2[j]; }
                else { dp2[j+k] += dp2[j]; }                
            }
            dp2[j] = -1;
        }
    }
    }
    
    for ( int i = 0; i < K; i++ ) {
    for ( int j = 6*N; j >= 0; j-- ) {
        if ( dp2[j] != -1 ) {
            for ( int k = 4; k <= 6; k++ ) {
                if ( dp2[j+k] == -1 ) { dp2[j+k] = dp2[j]; }
                else { dp2[j+k] += dp2[j]; }                
        }
            dp2[j] = -1;
        }
    }
    }
    
    
    
    // for ( int i = 1; i < 6*N+1; i++ ) {
        // cout << dp1[i] << " ";
        // if ( i%10 == 0 ) { cout << endl; }
    // }
    // cout << endl;
    // for ( int i = 1; i < 6*N+1; i++ ) {
        // cout << dp2[i] << " ";
        // if ( i%10 == 0 ) { cout << endl; }
    // }
    // cout << endl;
    
    long long ans = 0;
    for ( int i = 2; i < 6*N+1; i++ ) {
        
        if ( dp2[i] == -1 ) { continue; }
        
        long long s = 0;
        for ( int j = 1; j < i; j++ ) {
            if ( dp1[j] == -1 ) { continue; }
            s += dp1[j];
        }
        ans += s * dp2[i];
        
    }
    
    // cout << ans << endl;
    // cout << (pow(6,N)*pow(6,(N-K))*pow(3,K) ) << endl;
    
    printf( "%f", static_cast<double>(ans) / (pow(6,N)*pow(6,(N-K))*pow(3,K) ) );
    
    
    
    return 0;
}