using System;

namespace StudyApp
{
    class Program
    {
        static void Main(string[] args)
        {
            int enemy_num = int.Parse(Console.ReadLine());
            int[] items = new int[10];
            int powerUp = 0;

            for (int i = 0; i < enemy_num; i++)
            {
                string[] inputs = Console.ReadLine().Split(' ');
                foreach (var data in inputs)
                {
                    items[int.Parse(data) - 1] += 1;
                    if (items[int.Parse(data) - 1] >= 2)
                    {
                        powerUp++;
                        items[int.Parse(data) - 1] -= 2;
                    }
                }
            }

            int total = 0;
            foreach (var value in items)
            {
                total += value;
            }

            powerUp += total / 4;
            Console.WriteLine(powerUp);
        }
    }
}