#include <iostream>
#include <vector>
#include <algorithm>
using namespace std;

#define RREP(i,s,e) for (i = e-1; i >= s; i--)
#define rrep(i,n) RREP(i,0,n)
#define REP(i,s,e) for (i = s; i < e; i++)
#define rep(i,n) REP(i,0,n)
#define INF 1e8

typedef long long ll;

int main() {
    int i, j, l, n, k;
    ll dp[2][11][61] {};
    double ans = 0;
    cin >> n >> k;
    dp[0][0][0] = 1;
    REP (i,1,n+1) rep (j,55) REP (l,1,7)
        dp[0][i][j+l] += dp[0][i-1][j];
    rep (i,60) dp[0][n][i+1] += dp[0][n][i];
    dp[1][0][0] = 1;
    REP (i,1,k+1) rep (j,55) REP (l,4,7)
        dp[1][i][j+l] += 2 * dp[1][i-1][j];
    REP (i,k+1,n+1) rep (j,55) REP (l,1,7)
        dp[1][i][j+l] += dp[1][i-1][j];
    REP (i,1,61) ans += dp[0][n][i-1] * dp[1][n][i];
    ans /= dp[0][n][60] * accumulate(dp[1][n],dp[1][n]+61,0);
    cout << ans << endl;
    return 0;
}