import qualified Data.ByteString.Lazy.Char8 as C
import qualified Data.Map.Strict as M

counter :: C.ByteString -> M.Map Char Int
counter = C.foldr counter' M.empty
    where
        counter' x m
            | M.notMember x m = M.insert x 1 m
            | otherwise = M.adjust (+ 1) x m

countTrees :: C.ByteString -> Int
countTrees s = minimum [t, r, div e 2]
    where
        ctr = counter s
        t = M.findWithDefault 0 't' ctr
        r = M.findWithDefault 0 'r' ctr
        e = M.findWithDefault 0 'e' ctr

main :: IO ()
main = print . countTrees =<< C.getContents