module Main where

import Data.List
import Control.Monad
import Debug.Trace
import qualified Data.ByteString.Char8 as BC
import Data.Maybe (fromJust)
import qualified Data.Set  as S
import qualified Data.IntMap.Strict as IM
import Data.Char


readTuple2 :: IO (Int, Int)
readTuple2 = do
    [a, b] <- map (fst . fromJust . BC.readInt) . BC.words <$> BC.getLine
    return (a, b)

readTuple3 :: IO (Int, Int, Int)
readTuple3 = do
    [a, b, c] <- map (fst . fromJust . BC.readInt) . BC.words <$> BC.getLine
    return (a, b, c)

readInt :: IO Int
readInt = fst . fromJust . BC.readInt <$> BC.getLine

readInts :: IO [Int]
readInts = map (fst . fromJust . BC.readInt) . BC.words <$> BC.getLine

split :: (a -> Bool) -> [a] -> [[a]]
split f [] = []
split f as = let
    (fo, la) = span f as
    las = case la of
        [] -> []
        xs -> split f $ tail xs
    in
        case fo of
            [] -> las
            xs -> xs : las

solve :: Int -> [(Int, Int)] -> String
solve n m = 
    let
        nums = show <$> [10 ^ (n - 1)..(10 ^ n - 1)]
        takeKeta keta num 
            | keta > n = Nothing
            | otherwise =  Just $ digitToInt $ num !! (keta - 1)
        satisfy number = all (\(keta, num) -> takeKeta keta number == Just num) m
        ans = filter satisfy nums
    in
    case ans of
        [] -> "-1"
        (x:xs) -> x
    


main = do
    (n, m) <- readTuple2
    conds <- replicateM m readTuple2
    putStrLn $ solve n conds
