using System;
using System.Collections;
using System.Collections.Generic;
using System.Collections.Specialized;
using System.Linq;
using System.Numerics;

namespace AtCoderWorkspace
{
    public class Solver
    {
        public void Solve()
        {
            var cin = new Scanner();
            var n = cin.nextInt();
            var m = cin.nextInt();
            var list = new List<Tuple<int, int>>();
            for (int i = 0; i < m; i++)
            {
                var s = cin.nextInt();
                var c = cin.nextInt();
                list.Add(Tuple.Create(s, c));
            }

            var ss = new string[n];
            foreach (var item in list)
            {
                var digit = item.Item1 - 1;
                var num = item.Item2;

                if (ss[digit] != (num.ToString()) && ss[digit] != null)
                {
                    Console.WriteLine(-1);
                    return;
                }
            }


            var dd = new int[] { 0,0, 10, 100 };
            for (int nn = dd[n]; nn < 999; nn++)
            {
                if (n == 1 && nn == 10) break;
                if (n == 2 && nn == 100) break;

                var f = true;
                var set = new HashSet<int>();
                foreach (var item in list)
                {
                    var digit = item.Item1;
                    var num = item.Item2;
                    set.Add(digit);
                    var ns = nn.ToString().ToArray();
                    if (ns[digit - 1] != num.ToString().ToCharArray()[0]) f = false;
                }
                
                if(nn.ToString().Length == n && (f != false))
                {
                    Console.WriteLine(nn);
                    return;
                }
            }
            Console.WriteLine(-1);
        }
    }

    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);
            if (s.Length == 0) return next();
            i = 0;
            return s[i++];
        }

        public int nextInt()
        {
            return int.Parse(next());
        }
        public int[] ArrayInt(int N, int add = 0)
        {
            int[] Array = new int[N];
            for (int i = 0; i < N; i++)
            {
                Array[i] = nextInt() + add;
            }
            return Array;
        }

        public int[] DPArrayInt(int N, int ex)
        {
            int[] Array = new int[N + ex];
            for (int i = 0; i < N; i++)
            {
                Array[i] = nextInt();
            }
            return Array;
        }

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

        public long[] ArrayLong(int N, long add = 0)
        {
            long[] Array = new long[N];
            for (int i = 0; i < N; i++)
            {
                Array[i] = nextLong() + add;
            }
            return Array;
        }

        public long[] DPArrayLong(int N, int ex)
        {
            long[] Array = new long[N + ex];
            for (int i = 0; i < N; i++)
            {
                Array[i] = nextLong();
            }
            return Array;
        }

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


        public double[] ArrayDouble(int N, double add = 0)
        {
            double[] Array = new double[N];
            for (int i = 0; i < N; i++)
            {
                Array[i] = nextDouble() + add;
            }
            return Array;
        }
    }

    class Program
    {
        static void Main(string[] s) => new Solver().Solve();
    }
}



Measured memory_bytes: 13408