using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;

namespace AtCoder_solve
{
    class Program
    {
        public const ulong mod = 1000000007;

        static void Main(string[] args)

        {

            var data = Console.ReadLine().Split();
            var n = int.Parse(data[0]);
            var m = int.Parse(data[1]);
            var s = new List<int>();
            var c = new List<char>();
            string ans = "-1";
            bool judge = true;

            for(int i = 0; i < m; i++)
            {
                var data2 = Console.ReadLine().Split();
                s.Add(int.Parse(data2[0]));
                c.Add(char.Parse(data2[1]));

            }

            if (n == 1)
            {

                ans = ""+c[0];
                 for(int j = 0; j < m; j++)
                    {

                        if (c[j] != c[0]) ans = "-1";
                    }
                
            }

            if (n == 2)
            {
                for(int i = 1; i < 10; i++)
                {
                    for(int j = 0; j < 10; j++)
                    {
                        judge = true;
                        var num = "" + i + "" + j;

                        for(int k = 0; k < m; k++)
                        {
                            if (num[s[k]-1] != c[k]) judge = false; 
                        }
                        if (judge)
                        {
                            ans = num;
                            break;
                        }
                    }
                    if (judge) break;
                }
            }

            if (n == 3)
            {
                for (int h = 1; h < 10; h++)
                {
                    for (int i = 0; i < 10; i++)
                    {
                        for (int j = 0; j < 10; j++)
                        {
                            judge = true;
                            var num = ""+h+"" + i + "" + j;

                            for (int k = 0; k < m; k++)
                            {
                                if (num[s[k]-1] != c[k]) judge = false;
                            }
                            if (judge)
                            {
                                ans = num;
                                break;
                            }
                        }
                        if (judge) break;
                    }
                    if (judge) break;
                }
            }



            Console.WriteLine(ans);
        
            
        }
    }
}
