open System
open System.Text
open System.Collections.Generic

[<EntryPoint>]
let main argv =
  let n = Console.ReadLine() |> Int32.Parse
  let s = Console.ReadLine()

  let solve () =
    ["00"; "11"; "1010"; "0101"] |> List.exists (fun pattern -> s.IndexOf(pattern) >= 0)

  printfn "%s" <| (if solve () then "YES" else "NO")

  //exit
  0