#include <bits/stdc++.h>
using namespace std;

int main() {
	int n;
	cin>>n;
	
	vector<int> numbers(n);
	
	for(int i=0; i<n; i++){
		cin>>numbers[i];
	}
	
	int answer = 0;
	
	for(int i=0; i<n; i++){
		for(int j=i+1; j<n; j++){
			if((numbers[i] + numbers[j])%5 == 0)answer++;
		}
	}
	
	cout<<answer;
	
	return 0;
}