#include <bits/stdc++.h>
#define rep(i,n) for(int i = 0; i < (n); ++i)
#define srep(i,s,t) for (int i = s; i < t; ++i)
#define drep(i,n) for(int i = (n)-1; i >= 0; --i)
using namespace std;
typedef long long int ll;
typedef pair<int,int> P;
#define yn {puts("Yes");}else{puts("No");}
#define MAX_N 200005

int main() {
    int n, k;
    cin >> n >> k;
    int a[6] = {1,2,3,4,5,6};
    int b[6] = {4,4,5,5,6,6};

    ll f[70] = {};
    ll g[70] = {};

    ll m = 1;
    rep(i,n)m *= 6;

    rep(loop, m){
        int ii = loop;
        int h[n];
        rep(i,n){
            h[i] = ii % 6;
            ii /= 6;
        }
        int tmp1 = 0;
        int tmp2 = 0;
        rep(i,n){
            if(i < k)tmp1 += b[h[i]];
            else tmp1 += a[h[i]];
            tmp2 += a[h[i]];
        }
        f[tmp1]++;
        g[tmp2]++;
    }

    ll x = 0;
    ll y = m * m;

    rep(i,70){
        rep(j,i){
            x += f[i] * g[j];
        }
    }
    // cout << x << endl;
    double ans = (double)x / y;

    cout << ans << endl;
    return 0;
}