#include<stdio.h>

double JiShu(double x)
{
    double S = 1;
    int i = 1;
    /*if (x == 1)
    {
        return 2;
    }*/
   while(i <= x)
   {
       S = S + (1.00 / i);
       i++;
   }
    return S;
}
int main(void)
{
    double n;
    scanf_s("%lf",&n);
    if (JiShu(n) > n)
    {
        printf("%0.4lf\n", JiShu(n));
    }
    else
    {
        printf("不成立\n");
    }
    return 0;
}