import java.io.*;

class Main{

static final PrintWriter out=new PrintWriter(System.out);

public static void main(String[] args) throws IOException{
BufferedReader br=new BufferedReader(new InputStreamReader(System.in));
String line="";
while((line=br.readLine())!=null&&!line.isEmpty()){
int n=Integer.parseInt(line);
int t=Integer.parseInt(br.readLine());
double[][] dp1=new double[61][n+1];
double[][] dp2=new double[61][n+1];
dp1[0][0]=1;
dp2[0][0]=1;
for(int i=0;i<n;i++){
for(int j=0;j<=54;j++){
for(int k=1;k<=6;k++){
dp1[j+k][i+1]+=dp1[j][i]/6;
}
}
}
for(int i=0;i<t;i++){
for(int j=0;j<=54;j++){
for(int k=4;k<=6;k++){
dp2[j+k][i+1]+=dp2[j][i]/3;
}
}
}
for(int i=t;i<n;i++){
for(int j=0;j<=54;j++){
for(int k=1;k<=6;k++){
dp2[j+k][i+1]+=dp2[j][i]/6;
}
}
}
double ans=0;
for(int i=0;i<60;i++){
for(int j=i+1;j<=60;j++){
ans+=dp1[i][n]*dp2[j][n];
}
}
out.printf("%.20f\r\n", ans);
out.flush();
}
}
}