module Main where

import qualified Data.Map as M
import Data.List (find)
import qualified Data.Vector  as V

type Counts = M.Map Char Int
type Window = (Int, Int, Counts)

symbols :: [Char]
symbols = ['A', 'C', 'G', 'T']

initCounts :: Counts
initCounts = M.fromList [(c, 0) | c <- symbols]

getCounts :: String -> Counts
getCounts = foldl (\m c -> M.insertWith (+) c 1 m) initCounts

extras :: String -> Maybe Counts
extras [] = Nothing
extras s =
    let
        n = length s `div` 4  -- we're asured it's a multiple of 4
        acc0 = M.fromList [(c, 0) | c <- symbols]
        counts = getCounts s
        adjusted = M.map (\x -> x - n) counts
        es = M.filter (> 0) adjusted
     in
        case length es of
            0 -> Nothing  -- already balanced
            _ -> Just es  -- work to do

satisfied :: Counts -> Counts -> Bool
satisfied required actual = all (\c -> actual M.! c >= required M.! c) (M.keys required)

soln0 :: Counts -> String -> Maybe (Int, Counts)
soln0 es s = do
    let dists = drop 1 $ scanl (\m c -> M.insertWith (+) c 1 m) initCounts s
    let indexedDists = zip [0..] dists
    find (\(j, d) -> satisfied es d) indexedDists

slideUntilSuccess :: V.Vector Char -> Counts -> Window -> Maybe Window
slideUntilSuccess v required (i, j, counts) = do
    addC <- v V.!? (j + 1)  -- return Nothing if j + 1 is out of bounds
    let cminus = M.insertWith (+) (v V.! i) (-1) counts
    let counts' = M.insertWith (+) addC 1 cminus
    (if satisfied required counts' then Just (i + 1, j + 1, counts') else slideUntilSuccess v required (i + 1, j + 1, counts'))

shrinkUntilFail :: V.Vector Char -> Counts -> Window -> Window
shrinkUntilFail v required (i, j, counts) =
    if satisfied required counts
        then let counts' = M.insertWith (+) (v V.! i) (-1) counts
            in shrinkUntilFail v required (i + 1, j, counts')
        else (i, j, counts)

runner :: V.Vector Char -> Counts -> Window -> Window
runner v required w = do
    let w' = shrinkUntilFail v required w
    let w'' = slideUntilSuccess v required w'
    case w'' of
        Nothing -> w'
        Just ws -> runner v required ws

solve :: String -> Maybe Window
solve s = do
    es <- extras s
    (j0, dist0) <- soln0 es s
    let v = V.fromList s
    return $ runner v es (0, j0, dist0)

main :: IO ()
main = do
    n <- readLn :: IO Int
    s <- getLine
    case solve s of
        Nothing -> putStrLn "0"
        Just (i, j, _) -> print (j-i+2)