using System;
using static System.Console;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
using System.Diagnostics;
using System.Diagnostics.Contracts;

class Program
{
    static void Main()
    {
        var input = MyUtil.ReadintArray();
        var num = new int?[input[0]].Select<int?, int?>(x => null).ToArray();

        bool inv = false;

        for (int i = 0; i < input[1]; i++)
        {
            var line = MyUtil.ReadintArray();
            if (num[line[0] - 1] == null)
            {
                num[line[0] - 1] = line[1];
            }
            else
            {
                if (num[line[0] - 1] != line[1])
                {
                    inv = true;
                }
            }
        }

        if (num[0] == 0)
        {
            inv = true;
        }

        if (num.Length == 1)
        {
            if (num[0] == null)
            {
                num[0] = 0;
            }
        }
        else
        {
            if (num[0] == null)
            {
                num[0] = 1;
            }

            for (int i = 1; i < num.Length; i++)
            {
                if (num[i] == null)
                {
                    num[i] = 0;
                }
            }
        }

        var s = "";
        for (int i = 0; i < num.Length; i++)
        {
            s += ((int)num[i]).ToString();
        }

        Console.WriteLine(inv ? "-1" : s);
        ReadKey();
    }
}

static class MyUtil
{
    /// <summary>
    /// 指定の桁のビットを取得します。
    /// </summary>
    /// <param name="num"></param>
    /// <param name="count">取得する桁。</param>
    /// <returns></returns>
    public static int GetBit(this int num, int count)
    {
        int mask = (int)Math.Pow(2, count - 1);
        return (num & mask) == 0 ? 0 : 1;
    }

    /// <summary>
    /// <c>int</c>を2進数ビット配列に変換します。
    /// </summary>
    /// <param name="num"></param>
    /// <returns></returns>
    public static int[] ToBitArray(this int num)
    {
        const int size = sizeof(int) * 8;
        var array = new int[size];
        for (int i = 0; i < size; i++)
        {
            array[i] = num.GetBit(size - i);
        }
        return array;
    }

    public static long[] ReadlongArray()
    {
        return ReadLine().Split(' ').Select(s => long.Parse(s)).ToArray();
    }

    public static int[] ReadintArray()
    {
        return ReadLine().Split(' ').Select(s => int.Parse(s)).ToArray();
    }

    /// <summary>
    /// <see cref="IEnumerable{T}"/>の各要素を並べてコンソールに出力します。各要素の間には半角スペースが一つ入ります。
    /// </summary>
    /// <typeparam name="T"></typeparam>
    /// <param name="ts"></param>
    public static void WriteToConsole<T>(this IEnumerable<T> ts)
    {
        StringBuilder stringBuilder = new StringBuilder();
        foreach (T t in ts)
        {
            stringBuilder.Append(t.ToString());
            stringBuilder.Append(" ");
        }
        stringBuilder.Remove(stringBuilder.Length - 1, 1);
        Console.WriteLine(stringBuilder.ToString());
    }

    public static void WriteToDebugConsole<T>(this IEnumerable<T> ts)
    {
        StringBuilder stringBuilder = new StringBuilder();
        foreach (T t in ts)
        {
            stringBuilder.Append(t.ToString());
            stringBuilder.Append(" ");
        }
        stringBuilder.Remove(stringBuilder.Length - 1, 1);
        System.Diagnostics.Debug.WriteLine(stringBuilder.ToString());
    }
}
