import Data.List (group, sort)

getPowerUpNumber :: [Int] -> Int
getPowerUpNumber xs = p1 + p2
    where
        ys = map length $ group $ sort $ xs
        p1 = sum $ map (`div` 2) ys
        p2 = (`div` 4) $ sum $ map (`mod` 2) ys

main :: IO ()
main = print . getPowerUpNumber . map read . drop 1 . words =<< getContents