#include <stdio.h>
#include <stdlib.h>
#define MAX 101

int main()
{
    int n;
    scanf("%d",&n);

    float suma=0;
    int niza[MAX];
    for (int i=0;i<n;i++){
        scanf("%d", &niza[i]);
    }
    for(int i=n-1;i>0;i--)
    {
        suma=1/(suma+niza[i]);
    }
    printf("%f",(float) niza[0] + suma);

      /// niza = {1, 2 ,3, 4 ,5 }
      /// {0, 1, 2, 3, 4}

    return 0;

}