#include <stdio.h>

int main() {
    int n=0;
    double sum=0.0;
    int d=1;
    int sum1=0;
    scanf("%d",&n);
    for(int i=1;i<=2*n-1;i+=2)
    {
        sum1=sum1+i*d;
        d=-d;
        sum=sum+1.0/sum1;
    }
    printf("%.3f",sum);

    return 0;
}