//s = n * 1/1 + 2 * ((n-1) * 1/2 +(n-2) * 1/3 + ... + 1 * 1/n)
#include<iostream>
using namespace std;
int main()
{
double n;
while(scanf("%lf", &n) != EOF && n)
{
double s = 0;
int k = 1, i;
for(i = n; k < n; i --, k++)
{
s += (double)k * 1.0 /double(i);
}
s = s * 2.0 + n;
printf("%.2lf\n",s);
}
return 0;
}