using System;
using System.IO;
using System.Text;
using System.Linq;
using System.Collections;
using System.Collections.Generic;
using static System.Console;
using static System.Math;

namespace AtCoder
{

    public class Program
    {
        const long MOD = 1000000007;
        public static void Main(string[] args)
        {
            new Program().Solve(new ConsoleInput(Console.In, ' '));
        }

        public void Solve(ConsoleInput cin)
        {
            long N = cin.ReadLong;
            long M = cin.ReadLong;
            List<long> sList = new List<long>();
            List<long> cList = new List<long>();

            for (long j = 0; j < M; j++)
            {
                sList.Add(cin.ReadLong);
                cList.Add(cin.ReadLong);
            }
            for (long i=0;i<Pow(10,N);i++)
            {
                string str = i.ToString();
                int cnt = 0;
                for (int j = 0; j < M; j++)
                {
                    long s = sList[j];
                    long c = cList[j];
                    switch (s)
                    {
                        case 1:
                            if(str[0].ToString() == c.ToString())
                            {
                                cnt++;
                            }
                            break;
                        case 2:
                            if (str.Count() >= 2 && str[1].ToString() == c.ToString())
                            {
                                cnt++;
                            }
                            break;
                        case 3:
                            if(str.Count() >= 3 && str[2].ToString() == c.ToString())
                            {
                                cnt++;
                            }
                            break;
                    }
                }
                if(cnt == M && str.Count() == N)
                {
                    WriteLine(str);
                    return;
                }
            }
            WriteLine(-1);

        }


        static long Gcd(long p, long q)
        {
            if (p % q == 0) return q;
            return Gcd(q, p % q);
        }

        public class ConsoleInput
        {
            private readonly System.IO.TextReader _stream;
            private char _separator = ' ';
            private Queue<string> inputStream;
            public ConsoleInput(System.IO.TextReader stream, char separator = ' ')
            {
                this._separator = separator;
                this._stream = stream;
                inputStream = new Queue<string>();
            }
            public string Read
            {
                get
                {
                    if (inputStream.Count != 0) return inputStream.Dequeue();
                    string[] tmp = _stream.ReadLine().Split(_separator);
                    for (int i = 0; i < tmp.Length; ++i)
                        inputStream.Enqueue(tmp[i]);
                    return inputStream.Dequeue();
                }
            }
            public string ReadLine { get { return _stream.ReadLine(); } }
            public int ReadInt { get { return int.Parse(Read); } }
            public long ReadLong { get { return long.Parse(Read); } }
            public double ReadDouble { get { return double.Parse(Read); } }
            public string[] ReadStrArray(long N) { var ret = new string[N]; for (long i = 0; i < N; ++i) ret[i] = Read; return ret; }
            public int[] ReadIntArray(long N) { var ret = new int[N]; for (long i = 0; i < N; ++i) ret[i] = ReadInt; return ret; }
            public long[] ReadLongArray(long N) { var ret = new long[N]; for (long i = 0; i < N; ++i) ret[i] = ReadLong; return ret; }
        }

    }
}

Measured memory_bytes: 11348