#include <bits/stdc++.h>
#define REP(i,n,N) for(int i=(n);i<(int) N;i++)
#define p(s) cout<<(s)<<endl
using namespace std;

double dp1[15][100];
double dp2[15][100];
int main(void){
	int N,K;
	cin>>N>>K;
	dp1[0][0]=dp2[0][0]=1;
	REP(i,0,N)	REP(j,0,i*6+1)	REP(k,1,7)	dp1[i+1][j+k]+=dp1[i][j]/6.0;
	REP(i,0,N)	REP(j,0,i*6+1)	{
		if(i<K) REP(k,4,7)	dp2[i+1][j+k]+=dp2[i][j]/3.0;
		else REP(k,1,7)	dp2[i+1][j+k]+=dp2[i][j]/6.0;
	}
	double ans=0;
	REP(i,0,N*6+1) REP(j,i+1,N*6+1) ans+=dp1[N][i]*dp2[N][j];

	printf("%.5lf",ans);
	return 0;
}