#include <stdio.h>

int main() 
{
    int n;
    double sum,sum1=0;
    scanf("%d",&n);
    for(int i=1;i<=n;i++)
    {
        if(i%2==0)
        {
            sum=-2*i/2.0;
        
        }
        else
        {
            sum=-2*(i-1)/2.0+(2*i-1);
        }
        sum1+=1.0/sum;
    }
    printf("%.3lf",sum1);
}