#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;
	
	unordered_map<int,int> modFreq;
	
	for(int i=0; i<n; i++){
		if(modFreq.find((5 - numbers[i]%5)%5) != modFreq.end()){
			answer += modFreq[(5 - numbers[i]%5)%5];
		}
		
		modFreq[numbers[i]%5]++;
	}
	
	cout<<answer;
	
	return 0;
}