hdu 2156

#include <iostream>#include <stdio.h>using namespace std;int main(){int i,n;while(cin>>n&&n){double sum=0;sum+=n*1.00;for(i=2;i<=n;i++)sum+=1.00/i*(n-i+1)*2;printf("%.2lf\n",sum);}return 0;}// hdu2156