#include <stdio.h>

void main(void){
	int n = 0;
	scanf("%d",&n);
	int card[n];
	for(int i = 0; i < n ; i++){
		scanf("%d",&card[i]);
	}
	int count = 0;
	for(int i = 0;i < n;i++ ){
		if(card[i] == -1){
			continue;
		}
		for(int j = i+1 ;j < n;j++){
			if(card[i] == -1){
				continue;
			}
			if(card[i] == card[j]){
				card[i] = -1;
				card[j] = -1;
				count++;
				break;
			}
		}
	}
	printf("%d",count);
}