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

namespace ForATCODER
{
    public class Program
    {
        public static void Main(string[] args)
        {
            int ccc = 0;

            int[] d = s2iarray(Console.ReadLine().Split(' '));
            int N = (int)Math.Pow(10,d[0]-1);
            int max = (int)Math.Pow(10, d[0]);
            int[] d1 = new int[d[1]];
            char[] d2 = new char[d[1]];
            Dictionary<int, int> s = new Dictionary<int, int>();
            for(int i = 0; i < d[1];i++)
            {
                int[] dd = s2iarray(Console.ReadLine().Split(' '));
                d1[i] = dd[0];
                d2[i] = Convert.ToString(dd[1])[0];
            }
            if (d[0] == 1) N = 0;
            for (; N< max;N++)
            {
                String ss = N.ToString();
                int i = 0;
                for (; i < d[1];i++)
                {
                    if (ss[d1[i] - 1] != d2[i]) break;
                    else
                    {
                     //   RESULT(N);
                    }
                }
                if (i == d[1]) { RESULT(N); return; };
            }
            RESULT(-1);

        }
     public static bool checka(int[] a,int m)
        {
            int back = 1;
            for(int i = 0; i<a.Length;i++)
            {
                if(a[i] >=1 && a[i] <=m)
                {
if(a[i] >= back)
                    {
                        back = a[i];
                    }
                    else
                    {
                        return false;
                    }
                }
                else
                {
                    return false;
                }
            }
            return true;
        }
        public static ulong pow(int a, int b)
        {
            ulong res = 1;
            for (int i = 0; i < b; i++)
            {
                res *= (ulong)a;
            }
            return res;
        }
        static int s2i(String s)
        {
            return Convert.ToInt32(s);
        }
        static ulong s2l(String s)
        {
            return Convert.ToUInt64(s);
        }
        static void RESULT(double res)
        {
            Console.WriteLine(res);
        }
        static void RESULT(long res)
        {
            Console.WriteLine(res);
        }
        static void RESULT(ulong res)
        {
            Console.WriteLine(res);
        }
        static void RESULT(int res)
        {
            Console.WriteLine(res);
        }
        static void RESULT(String res)
        {
            Console.WriteLine(res);
        }
        static String[] ReadLineAll(int count)
        {
            String[] res = new String[count];
            for (int i = 0; i < count; i++)
            {
                res[i] = Console.ReadLine();
            }
            return res;
        }

        static int[] s2iarray(String[] src)
        {
            int len = src.Length;
            int[] res = new int[len];
            for (int i = 0; i < len; i++)
            {
                res[i] = Convert.ToInt32(src[i]);
            }
            return res;
        }
        static long[] s2larray(String[] src)
        {
            int len = src.Length;
            long[] res = new long[len];
            for (int i = 0; i < len; i++)
            {
                res[i] = Convert.ToInt64(src[i]);
            }
            return res;
        }
        static ulong[] s2larray2(String[] src)
        {
            int len = src.Length;
            ulong[] res = new ulong[len];
            for (int i = 0; i < len; i++)
            {
                res[i] = Convert.ToUInt64(src[i]);
            }
            return res;
        }
    }
}


Measured memory_bytes: 13152