open Batteries
(* 文字列をcharのlistにする *)
let explode s = List.init (String.length s) (String.get s)
let n = read_int ()
let s = read_line () |> explode |> Array.of_list
let rec loop1 i =  
  let rec loop2 i2 =
    let rec loop3 i3 ans =
      if i3 >= n then ans else 
      (* ここに処理を書く *)
        (
        if (s.(i2) != s.(i3)) && (s.(i) != s.(i3)) then (
          if (i3 - i2) != (i2 - i) then loop3 (i3+1) (ans+1) else loop3 (i3+1) ans
        ) else (
        loop3 (i3+1) ans))
    in if i2 >= n-1 then 0 else (
      if s.(i) = s.(i2) then loop2 (i2+1) else
      loop3 (i2+1) 0 + loop2 (i2+1)
    )
  in if i >= n-2 then 0 else (
    loop2 (i+1) + loop1 (i+1))


let _ = Printf.printf "%d\n" @@ loop1 0
