#include <bits/stdc++.h>
using namespace std;
 
int main() {
	int n ;
	cin>>n;
	int arr[n];
	for(int i = 0; i< n ; i++){
		cin>>arr[i];
	}
	int count = 0;
	unordered_map<int,int> mpp;
	for(int j = 0; j< n ; j++){
		int real = arr[j]%5;  // range --[ 0..4]
		int r =( 5-real) %5;
		count += mpp[r];
		
		
		mpp[arr[j]%5] = mpp[arr[j]%5] + 1;
	}
	cout << count;
 
    return 0;
}