#include <bits/stdc++.h>
using namespace std;
 
// Find total number of pairs (i,j), i < j,
// such that (nums[i] + nums[j]) %5 ==0
 
int main()
{
    int n;
 
    int res = 0;
 
    cin >> n;
 
    vector<int> ar;
 
    for (int i = 0; i < n; i++)
    {
        int y;
        cin >> y;
        ar.push_back(y);
    }
 
    unordered_map<int, int> mp;
 
 
    for (int j = 0; j < n; j++)
    {
       int real=ar[j]%5;
       int r=5-real;
      r=r%5; //when a[j]=0 '(real numbers)we search for 5 which doesn't exist 
        if(mp.find(r)!=mp.end())
        {
          res+=mp[r];
         }
        mp[real]++;
    }
 
    cout << res << endl;
 
    return 0;
}

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NgoyIDIgNSAwIDMgMw==

6
2 2 5 0 3 3