找规律
#include<stdio.h>
#include<stdlib.h>
#include<math.h>
int n;
double SUM( )
{
double sum = 0;
sum = n;
for( int i = 2; i <= n; ++i )
{
sum += ( n - i + 1 ) * 1.0 / i * 2;
}
return sum;
}
int main( )
{
while( scanf( "%d",&n ),n )
printf( "%.2lf\n",SUM( ) );
return 0;
}