let rec gcd a b = 
    match b with
    | 0.0 -> a
    | x -> gcd x (a % x)

let lcm a b = a * b / (gcd a b)

let allLcm xs =
    let rec inAllLcm n l =
        match l with
        | [] -> n
        | y :: ys -> inAllLcm (lcm y n) ys
    inAllLcm 1.0 xs

let n = int (stdin.ReadLine())
let a = stdin.ReadLine().Split() |> Array.map float |> List.ofArray
let s = allLcm a
let b = List.sumBy (fun x -> s / x) a
printfn "%f" (s / b)