#include <bits/stdc++.h>
#pragma GCC optimize("Ofast")
#pragma GCC optimize("unroll-loops")
#pragma GCC target("sse,sse2,sse3,ssse3,sse4,fma,abm,mmx,avx,avx2")
#define rep(i, n) for (int i = 0; i < (int)(n); i++)
#define rrep(i, n) for (int i = (int)(n - 1); i >= 0; i--)
#define all(x) (x).begin(), (x).end()
#define sz(x) int(x.size())
#define yn(joken) cout<<((joken) ? "Yes" : "No")<<"\n"
#define YN(joken) cout<<((joken) ? "YES" : "NO")<<"\n"
using namespace std;
using ll = long long;
using vi = vector<int>;
using vl = vector<ll>;
using vs = vector<string>;
using vc = vector<char>;
using vd = vector<double>;
using vld = vector<long double>;
using vvi = vector<vector<int>>;
using vvl = vector<vector<ll>>;
using vvs = vector<vector<string>>;
using vvc = vector<vector<char>>;
using vvd = vector<vector<double>>;
using vvld = vector<vector<long double>>;
using vvvi = vector<vector<vector<int>>>;
using vvvl = vector<vector<vector<ll>>>;
using vvvvi = vector<vector<vector<vector<int>>>>;
using vvvvl = vector<vector<vector<vector<ll>>>>;
using pii = pair<int,int>;
using pll = pair<ll,ll>;
const int INF = 1e9;
const ll LINF = 2e18;
template <class T>
bool chmax(T& a, const T& b) {
    if (a < b) {
        a = b;
        return 1;
    }
    return 0;
}
template <class T>
bool chmin(T& a, const T& b) {
    if (b < a) {
        a = b;
        return 1;
    }
    return 0;
}
bool ispow2(int i) { return i && (i & -i) == i; }
bool ispow2(ll i) { return i && (i & -i) == i; }
template <class T>
vector<T> make_vec(size_t a) {
    return vector<T>(a);
}
template <class T, class... Ts>
auto make_vec(size_t a, Ts... ts) {
    return vector<decltype(make_vec<T>(ts...))>(a, make_vec<T>(ts...));
}
template <typename T>
istream& operator>>(istream& is, vector<T>& v) {
    for (int i = 0; i < int(v.size()); i++) {
        is >> v[i];
    }
    return is;
}
template <typename T>
ostream& operator<<(ostream& os, const vector<T>& v) {
    for (int i = 0; i < int(v.size()); i++) {
        os << v[i];
        if (i < int(v.size()) - 1) os << ' ';
    }
    return os;
}

static uint32_t RandXor(){
    static uint32_t x=123456789;
    static uint32_t y=362436069;
    static uint32_t z=521288629;
    static uint32_t w=88675123;
    uint32_t t;
 
    t=x^(x<<11);
    x=y; y=z; z=w;
    return w=(w^(w>>19))^(t^(t>>8));
}

static double Rand01(){
    return (RandXor()+0.5)*(1.0/UINT_MAX);
}

void solve(){
    int N,K;
    cin>>N>>K;
    vld DP1(6*N+1),DP2(6*N+1);
    DP1[0]=1;
    DP2[0]=1;
    long double p=1;
    p/=6;
    rep(i,N){
        vld NDP1(6*N+1);
        rep(j,6*N+1){
            for(int k=1;k<=6;k++){
                if(j+k<=6*N) NDP1[j+k]+=DP1[j]*p;
            }
        }
        swap(DP1,NDP1);
    }
    rep(i,N-K){
        vld NDP2(6*N+1);
        rep(j,6*N+1){
            for(int k=1;k<=6;k++){
                if(j+k<=6*N) NDP2[j+k]+=DP2[j]*p;
            }
        }
        swap(DP2,NDP2);
    }
    rep(i,K){
        vld NDP2(6*N+1);
        rep(j,6*N+1){
            for(int k=4;k<=6;k++){
                if(j+k<=6*N) NDP2[j+k]+=DP2[j]*2*p;
            }
        }
        swap(DP2,NDP2);
    }
    long double ans=0;
    rep(i,6*N+1){
        for(int j=i+1;j<=6*N;j++){
            ans+=DP1[i]*DP2[j];
        }
    }
    cout<<fixed<<setprecision(12)<<ans<<endl;
}

int main(){
    cin.tie(nullptr);
    ios::sync_with_stdio(false);

    solve();
}