#include <bits/stdc++.h>
#include <atcoder/all>
using namespace std;
using namespace atcoder;
typedef long long int ll;
typedef long double ld;
#define FOR(i,l,r) for(ll i=l;i<r;i++)
#define REP(i,n) FOR(i,0,n)
#define RFOR(i,l,r) for(ll i=r-1;i>=l;i--)
#define RREP(i,n) RFOR(i,0,n)
#define ALL(x) x.begin(),x.end()
#define PA pair<ll,ll>
#define F first
#define S second
#define BS(A,x) binary_search(ALL(A),x)
#define LB(A,x) (ll)(lower_bound(ALL(A),x)-A.begin())
#define UB(A,x) (ll)(upper_bound(ALL(A),x)-A.begin())
#define COU(A,x) (UB(A,x)-LB(A,x))
template<typename T>using min_priority_queue=priority_queue<T,vector<T>,greater<T>>;
using mint=modint1000000007;
//using mint=modint998244353;
void chmax(ll&a,ll b){a=max(a,b);}
void chmin(ll&a,ll b){a=min(a,b);}
void print(vector<ll>&A){REP(i,A.size()){if(i)cout<<" ";cout<<A[i];}cout<<endl;}
ld dist(ld x1,ld y1,ld x2,ld y2){return sqrtl((x1-x2)*(x1-x2)+(y1-y2)*(y1-y2));}
int main(){
  int N,K;cin>>N>>K;
  vector<vector<ll>>Taro(N+1,vector<ll>(60)),Jiro(N+1,vector<ll>(60));
  Taro[0][0]=Jiro[0][0]=1;
  REP(i,N)REP(j,6)REP(k,60-j)Taro[i+1][k+j]+=Taro[i][k];
  //REP(i,15)cout<<Taro[N][i]<<" ";cout<<endl;
  REP(i,N-K+1)Jiro[i]=Taro[i];
  FOR(i,N-K,N)FOR(j,3,6)REP(k,60-j)Jiro[i+1][k+j]+=2*Jiro[i][k];
  //REP(i,15)cout<<Jiro[N][i]<<" ";cout<<endl;
  ll ans=0;
  REP(i,60)REP(j,i)ans+=Jiro[N][i]*Taro[N][j];
  printf("%.10llf\n",(ld)ans/powl(36,N));
  return 0;
}