open System
type Sol() =
    member this.Solve() = 
        let N = stdin.ReadLine() |> int
        let A = stdin.ReadLine().Split() |> Array.map int |> Array.sort
//        let ans = if (N%2) = 0 then double (A.[N/2]+A.[(N/2)-1])/2.0 else double A.[N/2]
//        printfn "%f" ans
        if (N%2) = 0 then double (A.[N/2]+A.[(N/2)-1])/2.0 else double A.[N/2]
        |> printfn "%f" 
let mySol = new Sol()
mySol.Solve()