#include <stdio.h>

int main() {
    int sum=0;
    double summ=0.0;
    int n;
    scanf("%d",&n);
    int t=1;
    for(int i=1;i<=2*n-1;i+=2)
    {
        int ii=i*t;
        sum+=ii;
        t=-t;
        summ+=1.0/sum;
    }
    printf("%.3f",summ);
    return 0;
}