using System;
using System.Collections.Generic;

namespace Yukicorder_029 {
    class Program{
        static void Main(string[] args) {
            int N = InputN(1, 100);
            int Level = 0;
            var list = new List<string>();
            var Items = new List<string>();
            for (int i = 0; i < N; i++) {
                list.AddRange(Console.ReadLine().Split());
            }
            foreach (String Match in list) {
                if(!Items.Contains(Match)) {
                    Items.Add(Match);
                }else{
                    Items.Remove(Match);
                    Level++;
                }
            }
            Level = Level + Items.Count / 4;

            Console.WriteLine(Level);
        }                               

        static int InputN(int Min , int Max) {
            int Number = int.Parse(Console.ReadLine());
            try {
                if(Number < Min || Number > Max) {
                    Console.WriteLine(Min + "以上" + Max + "以下で入力してください");
                }
            }catch(FormatException e) {
                Console.WriteLine("数字を入力してください");
            }catch(Exception E) {
                Console.WriteLine("想定外のエラーです");
            }
            return Number;
        } 
    }
}