import Data.List
 
substrings :: [a] -> [[a]]
substrings = ([]:) . concatMap (tail . inits) . tails

acgt :: [Char] -> Bool
acgt [] = True
acgt (x:xs)
        | x `elem` "ACGT" = acgt xs
        | otherwise = False
 
main = do
        s <- getLine
        print.maximum.map length $ filter acgt $ substrings s