#include <stdio.h>
#include <stdlib.h>
#include <stdbool.h>
#include <math.h>

// パワーアップ
int main()
{
	enum PowerUp
	{
		SAME_NEED = 2,
		WRONG_NEED = 4,
	};
	int input = 0;
	int item[100] = { 0 };
	int powerUp = 0;
	int cnt = 0;

	scanf("%d", &input);
	
	for (int i = 0;i < input;i++, cnt++)
	{
		int n = 0;
		bool flag = false;
		scanf("%d", &n);

		for (int j = 0;j <= i;j++)
		{
			if (item[j] == n)
			{
				item[j]++;
				flag = true;
				if (item[j] >= SAME_NEED)
				{
					item[j] -= SAME_NEED;
					cnt -= SAME_NEED;
					powerUp++;
				}
			}
		}
		
		if (!flag)
		{
			item[i] = n;
		}
	}

	powerUp += cnt / 4;

	printf("%d", powerUp);

	return 0;
}