Scanf.scanf "%d" (fun n ->
    let x = Array.init n (fun _ -> Scanf.scanf " %f" (fun x -> x)) in
    let xs = Array.fold_left (+.) 0. x in
    let av = xs /. float n in
    let rec loop i acc =
        if i = n then sqrt (acc /. float n) else
            let acc = acc +. (x.(i) -. av) *. (x.(i) -. av) in
            loop (i + 1) acc
    in
    let sq = loop 0 0. in

    Scanf.scanf " %d" (fun m ->
        if sq = 0. then print_endline "50" else
        let ans = int_of_float (floor (10. *. (x.(m - 1) -. av) /. sq +. 50.)) in
        Printf.printf "%d\n" ans
    )
)