#include <bits/stdc++.h>
using namespace std;
 
int main() {
	// your code goes here
	int n;
	cin>>n;
 
	vector<int> v(n);
	for(int i = 0; i < n; i++){
		cin>>v[i];
	}
 
	unordered_map<int,int> ump;
	int cnt = 0;
 
	for(int i = 0; i < n; i++){
 
		// Sometimes v[i] is greater then 5 then if we did not perform this step which 
		// leads to end up -ve numbers
 
		int ele = v[i] % 5;
 
		int rem = (5 - ele) % 5;
 
		if(ump.count(rem)){
			cnt += ump[rem];
		}
 
		ump[v[i] % 5] ++;
	}
	cout<<cnt<<endl;
	return 0;
}

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

NgoyCjIKNQo1CjMKMw==

6
2
2
5
5
3
3