{-# LANGUAGE
  ScopedTypeVariables, BangPatterns, TupleSections, ExplicitForAll,
  LambdaCase, MultiWayIf, Unsafe, RecordWildCards, FlexibleContexts, CPP,
  NoMonomorphismRestriction, GADTs,
  RankNTypes, EmptyDataDecls, EmptyCase, ViewPatterns #-}

import Data.Bits
import Data.List
import qualified Data.ByteString.Char8 as BS
import qualified Data.ByteString.Lazy.Char8 as BSL
import Data.IntMap.Strict (IntMap)
import qualified Data.IntMap.Strict as IMS
import qualified Data.IntMap.Lazy as IML
import Data.IntSet (IntSet)
import qualified Data.IntSet as IS
import qualified Data.Sequence as Seq
import Data.Sequence (Seq)
import qualified Data.Array.IArray as A
import qualified Data.Array.MArray.Safe as A
import qualified Data.Array.MArray as A
import Data.Array (Array)
import Data.Array.Unboxed (UArray)
import Data.Array.IArray (IArray)
import Data.Array.MArray.Safe (MArray)
import Data.Array.IO.Safe (IOArray, IOUArray)
import Data.Array.ST.Safe (STArray, STUArray, runSTArray, runSTUArray)
import qualified Data.Vector as V
import qualified Data.Vector.Unboxed as VU
import qualified Data.Vector.Unboxed.Mutable as VUM
import Control.Monad
import Control.Monad.ST
-- import Control.Monad.ST.Safe
import Control.Applicative
import Data.Maybe
import Data.Tuple
import Data.Ord
import Control.Monad.State.Strict
import Data.Int
import Data.Word
import System.IO
import Data.Function
import Control.Monad.Primitive
import qualified Data.Vector.Primitive.Mutable as VPM
import qualified Data.Vector.Generic.Mutable as VGM
import Data.STRef
import Data.IORef


data Tup5 = Tup {-# UNPACK #-} !Int
                {-# UNPACK #-} !Int
                {-# UNPACK #-} !Int
                {-# UNPACK #-} !Int
                {-# UNPACK #-} !Int

main :: IO ()
main = do
  n <- readInt <$> getLine
  as <- VU.unfoldrN n (runStateT rInt) <$> BSL.getContents
  print $ (\(Tup _ _ _ _ r0) -> r0) $
    VU.foldl'
    (\(Tup l0_ lev_ od_ rev_ r0_) a ->
        let l0  =   l0_  + a
            lev = min l0
                  $ lev_ + if | a == 0 -> 2 | even a -> 0 | otherwise -> 1
            od  = min lev
                  $ od_  + if odd a then 0 else 1
            rev = min od
                  $ rev_ + if | a == 0 -> 2 | even a -> 0 | otherwise -> 1
            r0  = min rev
                  $ r0_  + a
        in Tup l0 lev od rev r0) (Tup 0 0 0 0 0) as
  

rInt :: StateT BSL.ByteString Maybe Int
rInt = StateT $ BSL.readInt . BSL.dropWhile (<'!')

#define D(f,r,d) f::Integral a=>a->d;f=fromIntegral;r::String->d;r=read
#define C(f,r,g,h,d) D(f,r,d);g,h::RealFrac a=>a->d;g=floor;h=ceiling
C(_toInteger_,readInteger,floorInteger,ceilInteger,Integer)
C(toInt,readInt,floorInt,ceilInt,Int)
C(toI8,readI8,floorI8,ceilI8,Int8)
C(toI16,readI16,floorI16,ceilI16,Int16)
C(toI32,readI32,floorI32,ceilI32,Int32)
C(toI64,readI64,floorI64,ceilI64,Int64)
C(toWord,readWord,floorWord,ceilWord,Word)
C(toW8,readW8,floorW8,ceilW8,Word8)
C(toW16,readW16,floorW16,ceilW16,Word16)
C(toW32,readW32,floorW32,ceilW32,Word32)
C(toW64,readW64,floorW64,ceilW64,Word64)
D(toDouble,readDouble,Double)
D(toFloat,readFloat,Float)
#undef D
#undef C


#define N(f,g,a,m)\
  f :: forall e i s. (C(a,m)A.Ix i) => (i,i) -> e -> m (a i e); f=A.newArray;\
  g :: forall e i s. (C(a,m)A.Ix i) => (i,i) -> m (a i e); g=A.newArray_
#define C(a,m)
N(newIOA,newIOA_,IOArray,IO)
N(newSTA,newSTA_,STArray s,ST s)
#undef C
#define C(a,m) MArray (a) e (m), 
N(newIOUA,newIOUA_,IOUArray,IO)
N(newSTUA,newSTUA_,STUArray s,ST s)
#undef C
#undef N



Measured memory_bytes: 2300