using System;
using System.IO;
using System.Text;
using System.Linq;
using System.Collections;
using System.Collections.Generic;
using static System.Console;
using static System.Math;

namespace AtCoder
{

    public class Program
    {
        const long MOD = 1000000007;
        public static void Main(string[] args)
        {
            new Program().Solve(new ConsoleInput(Console.In, ' '));
        }

        public void Solve(ConsoleInput cin)
        {
            long N = cin.ReadLong;
            long M = cin.ReadLong;
            List<long> first = new List<long>();
            List<long> second = new List<long>();
            List<long> third  = new List<long>();
            for(long i=0; i<M; i++)
            {
                long s = cin.ReadLong;
                long c = cin.ReadLong;
                switch (s)
                {
                    case 1:
                        first.Add(c);
                        break;
                    case 2:
                        second.Add(c);
                        break;
                    case 3:
                        third.Add(c);
                        break;
                }
            }
            first.Sort();
            second.Sort();
            third.Sort();

            if((N == 3 && first.Count == 0) || (N == 2 && second.Count == 0) || (N == 1 && third.Count == 0))
            {
                WriteLine(-1);
                return;
            }
            if((N == 3 && first[0] == 0) || (N==2 && second[0] == 0))
            {
                WriteLine(-1);
                return;
            }

            switch(N)
            {
                case 3:
                    Write(first[0]);
                    if (second.Count != 0)
                    {
                        Write(second[0]);
                    }
                    else
                    {
                        Write(0);
                    }
                    if (third.Count != 0)
                    {
                        Write(third[0]);
                    }
                    else
                    {
                        Write(0);
                    }
                    break;
                case 2:
                    Write(second[0]);
                    if (third.Count != 0)
                    {
                        Write(third[0]);
                    }
                    else
                    {
                        Write(0);
                    }
                    break;
                case 1:
                    Write(third[0]);
                    break;
            }
        }


        static long Gcd(long p, long q)
        {
            if (p % q == 0) return q;
            return Gcd(q, p % q);
        }

        public class ConsoleInput
        {
            private readonly System.IO.TextReader _stream;
            private char _separator = ' ';
            private Queue<string> inputStream;
            public ConsoleInput(System.IO.TextReader stream, char separator = ' ')
            {
                this._separator = separator;
                this._stream = stream;
                inputStream = new Queue<string>();
            }
            public string Read
            {
                get
                {
                    if (inputStream.Count != 0) return inputStream.Dequeue();
                    string[] tmp = _stream.ReadLine().Split(_separator);
                    for (int i = 0; i < tmp.Length; ++i)
                        inputStream.Enqueue(tmp[i]);
                    return inputStream.Dequeue();
                }
            }
            public string ReadLine { get { return _stream.ReadLine(); } }
            public int ReadInt { get { return int.Parse(Read); } }
            public long ReadLong { get { return long.Parse(Read); } }
            public double ReadDouble { get { return double.Parse(Read); } }
            public string[] ReadStrArray(long N) { var ret = new string[N]; for (long i = 0; i < N; ++i) ret[i] = Read; return ret; }
            public int[] ReadIntArray(long N) { var ret = new int[N]; for (long i = 0; i < N; ++i) ret[i] = ReadInt; return ret; }
            public long[] ReadLongArray(long N) { var ret = new long[N]; for (long i = 0; i < N; ++i) ret[i] = ReadLong; return ret; }
        }

    }
}