using System;
using System.Collections.Generic;
using System.Linq;
namespace yuki924
{
    class Problem
    {

        public static List<string[]> getinputdata (){

            List<string[]> list_temp = new List<string[]>();
            string strdata = Console.ReadLine ();

            while (strdata!=null) {

                string[] s_temp = strdata.Split (' ');

                list_temp.Add (s_temp);

                strdata = Console.ReadLine ();

            }

            return list_temp;
        }

        public static void Wordcheck (int l,int r,ref string s){

            string temp = "";

            for(int i= r;i>=l;i--){


                temp += s[i].ToString();

            }

            Console.WriteLine(temp);

        }

        public static void Main (string[] args)
        {
            List<string[]> list_result = new List<string[]>();
            list_result = getinputdata();
            HashSet<string> hs = new HashSet<string>();

            int n =int.Parse(list_result[0][0]);


            for (int i = 1; i < 1 + n; i++)
            {
                hs.Add(list_result[i][0]);
            }

            if (hs.Count > 1)
            {
                Console.WriteLine("YES");
            }
            else
            {
                Console.WriteLine("NO");

            }


        }

    }
}