439A - Devu the Singer and Churu the Joker - CodeForces Solution

#include<bits/stdc++.h>
#define ll long long int
#define rep(i, a, b) for (ll i = a; i < b; i++)
#define pb push_back
#define ppb pop_back
#define pf push_front
#define ppf pop_front
#define ff first
#define ss second
#define as(v) v.begin(),v.end()
#define ds(v) v.rbegin(),v.rend()
#define mod 1000000007
#define dbgs(x) cout << #x << " " << x << endl;
#define dbgm(x) cout<<#x;cout<<" { ";rep(i,0,x.size()){cout<<x[i]<<" ";}cout<<"}";cout<<endl;
#define fast_io ios_base::sync_with_stdio(false);cin.tie(NULL)
using namespace std;

void solve() {
    ll n, m, d = 0; cin>> n >> m;
    rep(i, 0, n) {
        ll s; cin>> s;
        d += s;
    }
    d += (n - 1) * 10;
    if (d <= m) {
        cout<< (n - 1) * 2 + (m - d) / 5 << endl;
        return;
    }
    cout<< -1 << endl;
}
int main() {
    fast_io;
    ll t = 1;
    // cin>> t;
    while (t--) solve();
    return 0;
}