using System;
using System.Collections.Generic;
using System.Linq;

namespace AtCoder
{
    class Program
    {
        static void Main(string[] args)
        {
            input_iter = LazyLoadAllLines();
            //------------------------------------------------//
            //var n = Read<long>();
            //var s = Read();
            //var als = Read<long>(n);
            //var sls = Read(n);
            /*List<Tuple<string, long>> scls = new List<Tuple<string, long>>();
            for (int i = 0; i < m; ++i)
            {
                scls.Add(Tuple.Create(Read(), Read<long>()));
            }*/
            //List<List<long>> abls = new List<List<long>>();
            //List<long> cls = new List<long>();
            /*List<long> edgeNum = Enumerable.Repeat(0L, (int)n).ToList();
            for (int i = 0; i < n - 1; ++i)
            {
                abls.Add(Read<long>(2));
                abls[i].Add(i);
                abls[i].Add(-1);
                --abls[i][0];
                --abls[i][1];
                //cls.Add(Read<long>());
                ++edgeNum[(int)abls[i][0]];
                ++edgeNum[(int)abls[i][1]];
            }*/

            //als.Sort((l, r) => (r - l));
            //sls.Sort(StringComparer.OrdinalIgnoreCase);

            var n = Read<int>();
            var m = Read<long>();
            List<Tuple<int, int>> scls = new List<Tuple<int, int>>();
            for (int i = 0; i < m; ++i)
            {
                scls.Add(Tuple.Create(Read<int>(), Read<int>()));
            }

            int num = n == 1 ? 0 : (int)Math.Pow(10, n - 1);
            for(; num < (int)Math.Pow(10, n); ++num)
            {
                var s = num.ToString();
                if(scls.Select(sc => s[sc.Item1 - 1] == '0' + sc.Item2).All(val => val))
                {
                    Console.WriteLine(num);
                    return;
                }
            }

            Console.WriteLine(-1);
        }

        static IEnumerator<string> input_iter;

        static IEnumerator<string> LazyLoadAllLines(bool doSplit = true)
        {
            string line;
            if (doSplit)
            {
                do
                {
                    line = Console.ReadLine();
                    foreach (var s in line.Split(' '))
                        yield return s;
                } while (line != null);
            }
            else
            {
                do
                {
                    line = Console.ReadLine();
                    yield return line;
                } while (line != null);
            }
        }
        static _T Read<_T>() where _T : struct
        {
            input_iter.MoveNext();
            return (_T)Convert.ChangeType(input_iter.Current, typeof(_T));
        }
        static string Read()
        {
            input_iter.MoveNext();
            return input_iter.Current;
        }
        static List<_T> Read<_T>(long num) where _T : struct
        {
            List<_T> res = new List<_T>();
            for (long i = 0; i < num; ++i)
            {
                input_iter.MoveNext();
                res.Add((_T)Convert.ChangeType(input_iter.Current, typeof(_T)));
            }
            return res;
        }
        static List<string> Read(long num)
        {
            List<string> res = new List<string>();
            for (long i = 0; i < num; ++i)
            {
                input_iter.MoveNext();
                res.Add(input_iter.Current);
            }
            return res;
        }

    }
}


Measured memory_bytes: 13396