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

namespace ABC157C
{
    class Program
    {
        static void Main(string[] args)
        {
            string[] NM = Console.ReadLine().Split(' ');
            int N = int.Parse(NM[0]);
            int M = int.Parse(NM[1]);
            if (M == 0)
            {
                Console.WriteLine(-1);
            }
            else
            {
                int[] s = new int[M];
                int[] c = new int[M];
                for (int i = 0; i < M; i++)
                {
                    string[] sc = Console.ReadLine().Split(' ');
                    s[i] = int.Parse(sc[0]);
                    c[i] = int.Parse(sc[1]);
                }
                int[] num = new int[N];
                for (int i = 0; i < N; i++)
                {
                    num[i] = -1;
                }
                bool hantei = true;
                for (int i = 0; i < M; i++)
                {
                    if (num[s[i] - 1] == -1)
                    {
                        num[s[i] - 1] = c[i];
                    }
                    else if (num[s[i] - 1] == c[i])
                    {
                    }
                    else
                    {
                        hantei = false;
                    }
                }
                if (hantei == false | num[0] == 0)
                {
                    Console.WriteLine("-1");
                }
                else
                {
                    for (int i = 0; i < N; i++)
                    {
                        if (num[i] == -1)
                        {
                            if (i == 0)
                            {
                                num[i] = 1;
                            }
                            else
                            {
                                num[i] = 0;
                            }
                        }
                    }
                    Console.WriteLine(string.Join("", num));
                }
            }
        }
    }
}
