#include <bits/stdc++.h>
typedef long long ll;
using namespace std;
#define DUMP(x)  cout << #x << " = " << (x) << endl;
#define FOR(i, m, n) for(ll i = m; i < n; i++)
#define IFOR(i, m, n) for(ll i = n - 1; i >= m; i-- )
#define REP(i, n) FOR(i,0,n)
#define IREP(i, n) IFOR(i,0,n)
#define FOREACH(x,a) for(auto& (x) : (a) )
#define ALL(v) (v).begin(), (v).end()
#define SZ(x) ll(x.size())

int main(){
  ll N, K; cin >> N >> K;
  // px[i][j] = イカサマサイコロをi個振り，出た目の和がjとなる確率
  vector<vector<double>> px(K+1, vector<double>(6*K+1,0.0));
  px[0][0] = 1.0;
  REP(i,K) REP(j,6*i+1) FOR(k,4,7){
    px[i+1][j+k] += px[i][j]/3.0; 
  }
  // py[i][j] = 公平なサイコロをi個振り，出た目の和がjとなる確率
  vector<vector<double>> py(N+1, vector<double>(6*N+1,0.0));
  py[0][0] = 1.0;
  REP(i,N) REP(j,6*i+1) FOR(k,1,7) {
    py[i+1][j+k] += py[i][j]/6.0; 
  }
  double ans = 0.0;
  FOR(x,N+3*K,6*N+1){
    // 太郎 = xとなる確率，次郎 < xとなる確率
    double taro = 0.0, jiro = 0.0;
    FOR(y,1,x){
      jiro += py[N][y];
    }
    FOR(i,4*K,6*K+1) if(N-K<=x-i && x-i<=6*(N-K)){
      taro += px[K][i] * py[N-K][x-i];
    }
    ans += taro * jiro;
  }
  cout << fixed << setprecision(10) << ans << endl;
}