using System;
using System.Collections.Generic;
using System.Globalization;
using System.IO.Pipes;
using System.Linq;
using System.Security.Cryptography;
using System.Text;

namespace cswork
{
    class Program
    {
        class Scanner
        {
            string[] s;
            int i;

            char[] cs = new char[] { ' ' };

            public Scanner()
            {
                s = new string[0];
                i = 0;
            }

            public string next()
            {
                if (i < s.Length) return s[i++];
                string st = Console.ReadLine();
                while (st == "") st = Console.ReadLine();

                s = st.Split(cs, StringSplitOptions.RemoveEmptyEntries);
                i = 0;
                return next();
            }

            public int nextInt()
            {
                return int.Parse(next());
            }

            public long nextLong()
            {
                return long.Parse(next());
            }

            public double nextDouble()
            {
                return double.Parse(next());
            }
        }

        public Program() { }

        static void Main(string[] args)
        {
            new Program().Omame();
        }

        Scanner cin;
        const int MAXIN = 1024;
        bool[] used = new bool[MAXIN];
        int[] perm = new int[MAXIN];

        List<int[]> permList = new List<int[]>();

        public void Permutation(int pos, int n, int length)
        {
            if (pos == n)
            {
                permList.Add((int[])perm.Clone());
            }

            for (int i = 0; i < n; i++)
            {
                if (!used[i])
                {
                    perm[pos] = i;
                    used[i] = true;
                    Permutation(pos + 1, n, length);
                    used[i] = false;
                }
            }
        }

        void Omame()
        {
            cin = new Scanner();
            int N = cin.nextInt();
            int M = cin.nextInt();
            char[] ans = new char[N];
            for (int i = 0; i < N; i++)
            {
                ans[i] = 'x';
            }

            for (int i = 0; i < M; i++)
            {
                int s = cin.nextInt() - 1;
                string c = cin.next();
                if(ans[s] != 'x' && ans[s] != c[0])
                {
                    Console.WriteLine(-1);
                    return;
                }
                ans[s] = c[0];
            }

            string tmp = new string(ans);
            tmp = tmp.Replace('x', '0');
            if(tmp.Length != int.Parse(tmp).ToString().Length)
            {
                Console.WriteLine(-1);
            }
            else
            {
                Console.WriteLine(tmp);
            }
        }
    }
}
