{-# LANGUAGE BangPatterns      #-}
{-# LANGUAGE FlexibleInstances #-}
{-# LANGUAGE TupleSections     #-}

-- module Yukicoder.No1268 where

import           Control.Monad                     (when)
import           Data.Bits                         (Bits (unsafeShiftL, unsafeShiftR, (.&.), (.|.)))
import           Data.Char                         (isSpace)
import           Data.Coerce                       (coerce)
import qualified Data.Foldable                     as F
import           Data.IORef                        (modifyIORef', newIORef,
                                                    readIORef)
import           Data.Maybe                        (fromJust)
import           Data.Word                         (Word32, Word64, Word8)
import           Unsafe.Coerce                     (unsafeCoerce)

import qualified Data.ByteString                   as BS
import qualified Data.ByteString.Char8             as BSC8

import           Control.Monad.State               (StateT (..), modify', when)

import qualified Data.Vector.Fusion.Stream.Monadic as VFSM
import qualified Data.Vector.Unboxed               as VU
import qualified Data.Vector.Unboxed.Mutable       as VUM

main :: IO ()
main = do
  n <- readLn :: IO Int
  as <- seqInput n
  let ax = radixSortNonNegative as
  dp <- VUM.replicate (n + 1) 0 :: IO (VUM.IOVector Int)
  rev' n $ \i -> do
    when (i + 1 < n && (2 + ax VU.! i) == ax VU.! (i + 1)) $ do
      dpi1 <- VUM.unsafeRead dp (i + 1)
      VUM.unsafeWrite dp i (dpi1 + 1)
    when (i + 2 < n && (2 + ax VU.! i) == ax VU.! (i + 2)) $ do
      dpi2 <- VUM.unsafeRead dp (i + 2)
      VUM.unsafeWrite dp i (dpi2 + 1)
  ans <- newIORef n
  rep (n - 1) $ \i -> do
    when (ax VU.! i + 1 == ax VU.! (i + 1)) $ do
      dpi1 <- VUM.unsafeRead dp (i + 1)
      modifyIORef' ans (+ (dpi1 + 1))
  readIORef ans >>= print

stream :: Monad m => Int -> Int -> VFSM.Stream m Int
stream !l !r = VFSM.Stream step l
  where
    step x
      | x < r     = return $ VFSM.Yield x (x + 1)
      | otherwise = return VFSM.Done
    {-# INLINE [0] step #-}
{-# INLINE [1] stream #-}

rep, rep', rep1, rep1' :: Monad m => Int -> (Int -> m ()) -> m ()
rep n = flip VFSM.mapM_ (stream 0 n)
{-# INLINE rep #-}
rep' n = flip VFSM.mapM_ (stream 0 (n + 1))
{-# INLINE rep' #-}
rep1 n = flip VFSM.mapM_ (stream 1 n)
{-# INLINE rep1 #-}
rep1' n = flip VFSM.mapM_ (stream 1 (n + 1))
{-# INLINE rep1' #-}


streamR :: Monad m => Int -> Int -> VFSM.Stream m Int
streamR !l !r = VFSM.Stream step (r - 1)
  where
    step x
      | x >= l    = return $ VFSM.Yield x (x - 1)
      | otherwise = return VFSM.Done
    {-# INLINE [0] step #-}
{-# INLINE [1] streamR #-}

rev, rev', rev1, rev1' :: Monad m => Int -> (Int -> m ()) -> m ()
rev !n = flip VFSM.mapM_ (streamR 0 n)
{-# INLINE rev #-}
rev' !n = flip VFSM.mapM_ (streamR 0 (n + 1))
{-# INLINE rev' #-}
rev1 !n = flip VFSM.mapM_ (streamR 1 n)
{-# INLINE rev1 #-}
rev1' !n = flip VFSM.mapM_ (streamR 1 (n + 1))
{-# INLINE rev1' #-}

infixl 8 .<<., .>>.

(.<<.) :: Bits b => b -> Int -> b
(.<<.) = unsafeShiftL
{-# INLINE (.<<.) #-}

(.>>.) :: Bits b => b -> Int -> b
(.>>.) = unsafeShiftR
{-# INLINE (.>>.) #-}

class Word64Encode a where
  encode64 :: a -> Word64
  decode64 :: Word64 -> a
  encodeNonNegative64 :: a -> Word64
  encodeNonNegative64 = encode64
  decodeNonNegative64 :: Word64 -> a
  decodeNonNegative64 = decode64

instance Word64Encode Int where
  encode64 x = unsafeCoerce $ x + 0x3fffffffffffffff
  decode64 x = unsafeCoerce x - 0x3fffffffffffffff
  encodeNonNegative64 = unsafeCoerce
  decodeNonNegative64 = unsafeCoerce

instance Word64Encode (Int, Int) where
  encode64 (x, y) = unsafeCoerce
    $ (x + 0x3fffffff) .<<. 31 .|. (y + 0x3fffffff)
  decode64 xy = unsafeCoerce (x, y)
    where
      !x = xy .>>. 31 - 0x3fffffff
      !y = (xy .&. 0x7fffffff) - 0x3fffffff
  encodeNonNegative64 (x, y) = unsafeCoerce $ x .<<. 31 .|. y
  decodeNonNegative64 xy     = unsafeCoerce (x, y)
    where
      !x = xy .>>. 31
      !y = xy .&. 0x7fffffff

instance Word64Encode (Int, Int, Int) where
  encode64 (x, y, z) = unsafeCoerce $ ((x + 0xfffff) .<<. 21 .|. (y + 0xfffff)) .<<. 21 .|. (z + 0xfffff)
  decode64 xyz = unsafeCoerce (x, y, z)
    where
      !x = xyz .>>. 42 - 0xfffff
      !y = (xyz .>>. 21 .&. 0x1fffff) - 0xfffff
      !z = xyz .&. 0x1fffff - 0xfffff
  encodeNonNegative64 (x, y, z) = unsafeCoerce $ (x .<<. 21 .|. y) .<<. 21 .|. z
  decodeNonNegative64 xyz = unsafeCoerce (x, y, z)
    where
      !x = xyz .>>. 42
      !y = xyz .>>. 21 .&. 0x1fffff
      !z = xyz .&. 0x1fffff

radixSortInt :: VU.Vector Int -> VU.Vector Int
radixSortInt = unsafeCoerce . radixSort64 . unsafeCoerce

radixSort64 :: VU.Vector Word64 -> VU.Vector Word64
radixSort64 vword = F.foldl' step vword [0,16,32,48]
  where
    mask k x = fromIntegral $ x .>>. k .&. 0xffff
    step v k = VU.create $ do
      pref <- VU.unsafeThaw
            . VU.prescanl' (+) 0
            . VU.unsafeAccumulate (+) (VU.replicate 0x10000 0)
            $ VU.map ((, 1) . mask k) v
      res <- VUM.unsafeNew $ VU.length v
      VU.forM_ v $ \x -> do
        let !masked = mask k x
        i <- VUM.unsafeRead pref masked
        VUM.unsafeWrite pref masked $ i + 1
        VUM.unsafeWrite res i x
      return res
{-# INLINE radixSort64 #-}


radixSort :: (VU.Unbox a, Word64Encode a) => VU.Vector a -> VU.Vector a
radixSort = VU.map decode64 . radixSort64 . VU.map encode64
{-# INLINE radixSort #-}

radixSortNonNegative :: (VU.Unbox a, Word64Encode a) => VU.Vector a -> VU.Vector a
radixSortNonNegative
    = VU.map decodeNonNegative64 . radixSort64 . VU.map encodeNonNegative64
{-# INLINE radixSortNonNegative #-}

radixSort32 :: VU.Vector Word32 -> VU.Vector Word32
radixSort32 vec = F.foldl' step vec [0, 16]
  where
    mask k x = fromIntegral $ x .>>. k .&. 0xffff
    step v k = VU.create $ do
      pref <- VU.unsafeThaw
            . VU.prescanl' (+) 0
            . VU.unsafeAccumulate (+) (VU.replicate 0x10000 0)
            $ VU.map ((, 1) . mask k) v
      res <- VUM.unsafeNew $ VU.length v
      VU.forM_ v $ \x -> do
        let !masked = mask k x
        i <- VUM.unsafeRead pref masked
        VUM.unsafeWrite pref masked $ i + 1
        VUM.unsafeWrite res i x
      return res
{-# INLINE radixSort32 #-}

compress :: VU.Vector Int -> VU.Vector Int
compress vec = VU.create $ do
  mvec <- VUM.unsafeNew (VU.length vec)
  VU.mapM_ (\(i, x) -> VUM.unsafeWrite mvec (x .&. 0xffffffff) i)
    . VU.postscanl' (\(!i, !x) y ->
        if x .>>. 32 == y .>>. 32
          then (i, y)
          else (i + 1, y)
      ) (-1, -1)
    . radixSortInt
    $ VU.imap (\i x -> x .<<. 32 .|. i) vec
  return mvec
{-# INLINE compress #-}

type Parser a = StateT BSC8.ByteString Maybe a
runParser :: Parser a -> BSC8.ByteString -> Maybe (a, BSC8.ByteString)
runParser = runStateT
{-# INLINE runParser #-}
int :: Parser Int
int = coerce $ BSC8.readInt . BSC8.dropWhile isSpace
{-# INLINE int #-}
int1 :: Parser Int
int1 = fmap (subtract 1) int
{-# INLINE int1 #-}
char :: Parser Char
char = coerce BSC8.uncons
{-# INLINE char #-}
byte :: Parser Word8
byte = coerce BS.uncons
{-# INLINE byte #-}
skipSpaces :: Parser ()
skipSpaces = modify' (BSC8.dropWhile isSpace)
{-# INLINE skipSpaces #-}
seqInput :: Int -> IO (VU.Vector Int)
seqInput n = VU.unfoldrN n (runParser int) <$> BSC8.getLine
{-# INLINE seqInput #-}
parseN1 :: Int -> IO (VU.Vector Int)
parseN1 n = VU.unfoldrN n (runParser int) <$> BSC8.getContents
{-# INLINE parseN1 #-}
parseN2 :: Int -> IO (VU.Vector (Int, Int))
parseN2 n = VU.unfoldrN n (runParser $ (,) <$> int <*> int) <$> BSC8.getContents
{-# INLINE parseN2 #-}
parseN3 :: Int -> IO (VU.Vector (Int, Int, Int))
parseN3 n = VU.unfoldrN n (runParser $ (,,) <$> int <*> int <*> int) <$> BSC8.getContents
{-# INLINE parseN3 #-}
parseN4 :: Int -> IO (VU.Vector (Int, Int, Int, Int))
parseN4 n = VU.unfoldrN n (runParser $ (,,,) <$> int <*> int <*> int <*> int) <$> BSC8.getContents
{-# INLINE parseN4 #-}
parseN5 :: Int -> IO (VU.Vector (Int, Int, Int, Int, Int))
parseN5 n = VU.unfoldrN n (runParser $ (,,,,) <$> int <*> int <*> int <*> int <*> int) <$> BSC8.getContents
{-# INLINE parseN5 #-}
parseANBN :: Int -> IO (VU.Vector Int, VU.Vector Int)
parseANBN n = VU.unzip . VU.unfoldrN n (runParser $ (,) <$> int <*> int) <$> BSC8.getContents
{-# INLINE parseANBN #-}
parseANBNCN :: Int -> IO (VU.Vector Int, VU.Vector Int, VU.Vector Int)
parseANBNCN n = VU.unzip3 . VU.unfoldrN n (runParser $ (,,) <$> int <*> int <*> int) <$> BSC8.getContents
{-# INLINE parseANBNCN #-}

readInt :: BSC8.ByteString -> Int
readInt = fst . fromJust . BSC8.readInt
{-# INLINE readInt #-}
getInt :: IO Int
getInt = readInt <$> BSC8.getLine
{-# INLINE getInt #-}
readIntList :: BSC8.ByteString -> [Int]
readIntList = map readInt . BSC8.words
{-# INLINE readIntList #-}
getIntList :: IO [Int]
getIntList = readIntList <$> BSC8.getLine
{-# INLINE getIntList #-}
readInteger :: BSC8.ByteString -> Integer
readInteger = fst . fromJust . BSC8.readInteger
{-# INLINE readInteger #-}
getInteger :: IO Integer
getInteger = readInteger <$> BSC8.getLine
{-# INLINE getInteger #-}
readIntegerList :: BSC8.ByteString -> [Integer]
readIntegerList = map readInteger . BSC8.words
{-# INLINE readIntegerList #-}
getIntegerList :: IO [Integer]
getIntegerList = readIntegerList <$> BSC8.getLine
{-# INLINE getIntegerList #-}