#include <bits/stdc++.h>   using namespace std;   bool prime(long long n) {     for (int i = 2; i <= sqrt(n); i++)       if (n % i == 0) return false;     return true;   }   int main() {     string s, s1;     long long a, b, c, m, n, k, t, l, d, p, nl, np;     t = 1;     while (t--) {       cin >> n >> d;       vector<long long> arr(n);       long long sum = 0;       for (int i = 0; i < n; i++) {         cin >> arr[i];         sum += arr[i];       }       if (sum + (n - 1) * 10 > d)         cout << -1 << endl;       else {         cout << (n - 1) * 2 + (d - (sum + (n - 1) * 10)) / 5 << endl;       }     }   }   