HOJ ( acm.hdu.edu.cn ) 2156

#include<iostream>
using namespace std;
int main()
{
   double x;
   int n;
   cout.precision(2);
   while(cin>>n&&n!=0)
   {
       x=n;
       for(int i=2;i<=n;i++)
           x+=1.0/i*2*(n+1-i);
       cout<<fixed<<x<<endl;
   }
   return 0;
}