import Data.List
main::IO()
main = do
  n<-fmap read getLine
  xxs<-fmap(map words) . sequence . replicate n $getLine
  print . ( (+) <$> (sum . map (`div` 2)) <*> ((`div` 4) . sum . map (`mod` 2))) 
    . map length . group . sort . concat $xxs