using System;

public class Program {
	public static void Main(string[] args) {
		int n = int.Parse(Console.ReadLine());
		int[] item = new int[10];
		for (int i = 0; i < n; i++) {
			string[] s = Console.ReadLine().Split(' ');
			for (int j = 0; j < s.Length; j++) {
				item[int.Parse(s[j])-1]++;
			}
		}
		
		int level = 0;
		int count = 0;
		for (int i = 0; i < item.Length; i++) {
			level += item[i] / 2;
			count += item[i] % 2;
		}
		level += count / 4;
		
		Console.WriteLine(level);
	}
}