module IntSet = Set.Make (struct
  type t = int
  let compare = compare
end)

let rec upper_bound l r p =
  if r - l <= 1
  then l
  else let m = (l + r) / 2 in
       if p m 
       then upper_bound m r p
       else upper_bound l m p

let rec power ( * ) e m n =
  if n <= 0 then e
  else power ( * ) (if n land 1 = 0 then e else m * e) (m * m) (n lsr 1)

let modulo = 999999937
let ( +^ ) x y = (x + y) mod modulo
let ( -^ ) x y = x +^ (modulo - y)
let ( *^ ) x y = (x * y) mod modulo
let code c = Char.code c - Char.code 'a'

let hash = Array.fold_left (fun h c -> 26 *^ h +^ code c) 0

exception Exists

let () = Scanf.scanf "%d\n%s" @@ fun n s ->
  Printf.printf "%d\n" @@
  upper_bound 0 (n / 2 + 1) @@ fun l ->
    let radix = power ( *^ ) 1 26 l in
    let h = ref @@ hash @@ Array.init l @@ String.get s in
    let h' = ref @@ hash @@ Array.init l @@ fun i -> s.[i + l] in
    let set = ref @@ IntSet.singleton !h in
    try
      if IntSet.mem !h' !set then raise Exists;
      for i = 0 to n - 2 * l - 1 do
        h := 26 *^ !h +^ code s.[i + l] -^ radix *^ code s.[i];
        h' := 26 *^ !h' +^ code s.[i + 2 * l] -^ radix *^ code s.[i + l];
        set := IntSet.add !h !set;
        if IntSet.mem !h' !set then raise Exists;
      done; false
    with Exists -> true
