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

class Program
{
    public void Proc()
    {
        Reader.IsDebug = false;
        int lineCount = int.Parse(Reader.ReadLine());
        int inputCount = int.Parse(Reader.ReadLine());

        Dictionary<int, int> dic = new Dictionary<int, int>();

        List<int> numList = new List<int>();
        int ans = lineCount;
        for (int i = 1; i <= lineCount; i++)
        {
            numList.Add(i-1);
        }

        List<AmidaLine> amidaList = new List<AmidaLine>();
        for (int i = 0; i < inputCount; i++)
        {
            int[] inpt = Reader.GetInt();
            AmidaLine al = new AmidaLine(inpt[0]-1, inpt[1]-1, i);
            amidaList.Add(al);
        }

        for (int i = 0; i < lineCount; i++)
        {
            int pos = -1;
            int idx = i;
            for (int j = 0; j < inputCount; j++)
            {
                List<AmidaLine> select = new List<AmidaLine>(amidaList.FindAll(a => (a.Line1 == idx || a.Line2 == idx) && a.Pos > pos).OrderBy(b => b.Pos));
                if (select.Count == 0)
                {
                    break;
                }
                pos = select[0].Pos;
                idx = select[0].Goto(idx);
            }
            dic.Add(i, idx);
        }

        for (int i = 0; i < lineCount; i++)
        {
            int[] conv = new int[lineCount];
            for (int j = 0; j < numList.Count; j++)
            {
                conv[dic[j]] = numList[j];
            }
            numList.Clear();
            numList.AddRange(conv);

            bool isMatch = true;
            for (int j = 0; j < numList.Count; j++)
            {
                if (j != numList[j])
                {
                    isMatch = false;
                    break;
                }
            }
            if (isMatch)
            {
                ans = i + 1;
                break;
            }
        }
        Console.WriteLine(ans);

    }


    public class AmidaLine
    {
        public int Line1;
        public int Line2;
        public int Pos;
        public int Goto(int from)
        {
            if (from == Line1)
            {
                return Line2;
            }
            return Line1;
        }
        public AmidaLine(int l1, int l2, int p)
        {
            this.Line2 = l2;
            this.Line1 = l1;
            this.Pos = p;
        }
    }


    public class Reader
    {
        public static bool IsDebug = true;
        private static String PlainInput = @"


4
6
1 2
2 3
3 4
3 4
2 3
1 2



 
";
        private static System.IO.StringReader Sr = null;
        public static string ReadLine()
        {
            if (IsDebug)
            {
                if (Sr == null)
                {
                    Sr = new System.IO.StringReader(PlainInput.Trim());
                }
                return Sr.ReadLine();
            }
            else
            {
                return Console.ReadLine();
            }
        }
        public static int[] GetInt(char delimiter = ' ', bool trim = false)
        {
            string inptStr = ReadLine();
            if (trim)
            {
                inptStr = inptStr.Trim();
            }
            string[] inpt = inptStr.Split(delimiter);
            int[] ret = new int[inpt.Length];
            for (int i = 0; i < inpt.Length; i++)
            {
                ret[i] = int.Parse(inpt[i]);
            }
            return ret;
        }
    }
    static void Main()
    {
        Program prg = new Program();
        prg.Proc();
    }
}