#include <bits/stdc++.h>
//#include<boost/multiprecision/cpp_int.hpp>
//#include<boost/multiprecision/cpp_dec_float.hpp>
//#include <atcoder/all>
#define rep(i, a) for (int i = (int)0; i < (int)a; ++i)
#define rrep(i, a) for (int i = (int)a - 1; i >= 0; --i)
#define REP(i, a, b) for (int i = (int)a; i < (int)b; ++i)
#define RREP(i, a, b) for (int i = (int)a - 1; i >= b; --i)
#define pb push_back
#define eb emplace_back
#define all(x) x.begin(), x.end()
#define rall(x) x.rbegin(), x.rend()
#define popcount __builtin_popcount
#define first fi
#define second se
using ll = long long;
constexpr ll mod = 1e9 + 7;
constexpr ll INF = 1LL << 60;

// #pragma GCC target("avx2")
// #pragma GCC optimize("O3")
// #pragma GCC optimize("unroll-loops")

//using lll=boost::multiprecision::cpp_int;
//using Double=boost::multiprecision::number<boost::multiprecision::cpp_dec_float<1024>>;//仮数部が1024桁
template <class T>
inline bool chmin(T &a, T b)
{
	if (a > b)
	{
		a = b;
		return true;
	}
	return false;
}
template <class T>
inline bool chmax(T &a, T b)
{
	if (a < b)
	{
		a = b;
		return true;
	}
	return false;
}

template <typename T>
T mypow(T x, T n, const T &p = -1)
{ //x^nをmodで割った余り

	if(p!=-1){
		x%=p;
	}
	T ret = 1;
	while (n > 0)
	{
		if (n & 1)
		{
			if (p != -1)
				ret = (ret * x) % p;
			else
				ret *= x;
		}
		if (p != -1)
			x = (x * x) % p;
		else
			x *= x;
		n >>= 1;
	}
	return ret;
}

using namespace std;
//using namespace atcoder;


void solve()
{	
	int n,k;
	cin>>n>>k;

	vector<vector<ll>>dp(n+1,vector<ll>(n*6+5)),dp2(n+1,vector<ll>(n*6+5));
	dp[0][0]=1;dp2[0][0]=1;
	rep(i,n){
		for(int j=0;j<=i*6;++j){
			rep(x,6){
				if(j+x+1<=n*6)dp[i+1][j+(x+1)]+=dp[i][j];
			}
		}
	}
	rep(i,n-k){
		for(int j=0;j<=n*6;++j){
			rep(x,6){
				if(j+x+1<=n*6)dp2[i+1][j+(x+1)]+=dp2[i][j];
			}
		}
	}
	rep(i,k){
		for(int j=0;j<=n*6;++j){
			for(int x=3;x<6;++x){
				if(j+x+1<=n*6)dp2[n-k+i+1][j+(x+1)]+=dp2[n-k+i][j]*2;
			}
		}
	}
	double ans=0;
	for(int i=1;i<=n*6;++i){
		for(int j=i+1;j<=n*6;++j){
			ans+=dp[n][i]*dp2[n][j];
		}
	}
	ans/=pow(6,n*2);
	cout<<ans<<"\n";
}

int main()
{
	ios::sync_with_stdio(false);
	cin.tie(nullptr);
	cout << fixed << setprecision(15);
	solve();
	return 0;
}