include

include

using namespace std;

int main()
{
int i,x;
float s,n;
cin>>n>>x;
s=1;
for(i=1;i<=n;i++)
{
if(i%2!=0)
s=s+1/(2*i);

    else

       s= s+x/(n-i+1);
    }
cout<<fixed<<setprecision(2)<< s;



return 0;

}