using System;
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
    {
        public static void Main(string[] args)
        {
            new Program().Solve(new ConsoleInput(Console.In,' '));
        }

        public void Solve(ConsoleInput cin)
        {
            var N = cin.ReadInt;
            var M = cin.ReadInt;
            var Num = new string[N];
            for (var i = 0; i< N; i++) 
            {
                Num[i] = "0";
            }

            var ans = "";
            var Selected = new int[N];
            for (var i = 0; i < M; i++) 
            {
                var s = cin.ReadInt;
                var c = cin.ReadInt;
                if (s == 1 && c == 0) 
                {
                    ans = "-1";
                    break;
                }
                if (Selected[s - 1] == 1)
                {
                    ans = "-1";
                    break;
                }
                Selected[s - 1] = 1;
                Num[s-1] = c.ToString(); 
            }
            if (!ans.Equals("-1")) 
            {
                ans = "";
                if (Num[0].Equals("0")) ans = "1";
                else ans = Num[0];
                for (var i = 1; i < N; i++)
                {
                    ans += Num[i];
                }
            }

            WriteLine(ans);

        }
    }


    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;}
    }

}