{-# LANGUAGE BangPatterns #-}
{-# LANGUAGE BinaryLiterals #-}
{-# LANGUAGE MultiWayIf #-}
{-# LANGUAGE NumDecimals #-}
{-# LANGUAGE ScopedTypeVariables #-}
{-# LANGUAGE TupleSections #-}

import Control.Applicative
import Control.Arrow
import Control.Monad
import Control.Monad.ST

import Data.Char
import Data.List
import Data.Maybe

import qualified Data.ByteString.Char8 as B

import Data.Array.ST.Safe
import Data.STRef

import Debug.Trace
import Text.Printf

readInt = readLn :: IO Int
readInteger = readLn :: IO Integer
readInts = map ( fst . fromJust . B.readInt ) . B.words <$> B.getLine
readIntegers = map ( fst . fromJust . B.readInteger ) . B.words <$> B.getLine

which a b f = if f then a else b
mp [ a, b ] = ( a, b )

modifyArray a i f = writeArray a i =<< f <$> readArray a i

main = do
	[ n, m ] <- readInts
	[ ss, cs ] <- transpose . ( [ 0, 0 ] : ) <$> replicateM m readInts
	print $ fromMaybe (-1) $ listToMaybe $ do
		i <- [ 1 .. 1000 ]
		let
			str = map digitToInt $ show i
		guard $ length str == n && maximum ss <= length str && check ( map pred ss ) cs str
		return i

check ss cs str = runST $ do
	res <- newSTRef True
	forM_ ( zip ss cs ) $ \( s, c ) -> do
		modifySTRef res ( && ( s == -1 || ( str !! s ) == c ) )
	readSTRef res