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

class Program
{
    static string InputPattern = "Input4";

    static List<string> GetInputList()
    {
        var WillReturn = new List<string>();

        if (InputPattern == "Input1") {
            WillReturn.Add("5");
            WillReturn.Add("1 2 3");
            WillReturn.Add("4 5 6");
            WillReturn.Add("7 8 9");
            WillReturn.Add("10 1 2");
            WillReturn.Add("3 4 5");
        }
        else if (InputPattern == "Input2") {
            WillReturn.Add("3");
            WillReturn.Add("1 1 1");
            WillReturn.Add("1 1 1");
            WillReturn.Add("1 1 1");
        }
        else if (InputPattern == "Input3") {
            WillReturn.Add("3");
            WillReturn.Add("1 2 3");
            WillReturn.Add("5 4 1");
            WillReturn.Add("1 9 2");
        }
        else {
            string wkStr;
            while ((wkStr = Console.ReadLine()) != null) WillReturn.Add(wkStr);
        }
        return WillReturn;
    }

    static void Main()
    {
        List<string> InputList = GetInputList();

        IEnumerable<int> EnumItem =
            InputList.Skip(1).SelectMany(X => X.Split(' '), (X, Y) => int.Parse(Y));

        int PowerUpCnt = 0;

        //アイテムごとのCountを求める
        var Query = EnumItem.GroupBy(X => X).Select(X => new { X.Key, cnt = X.Count() });

        //同じアイテムが2つあればパワーアップ
        PowerUpCnt += Query.Sum(X => X.cnt / 2);

        //アイテムを4つ使ってパワーアップ
        PowerUpCnt += Query.Sum(X => X.cnt % 2) / 4;

        Console.WriteLine(PowerUpCnt);
    }
}