#include <bits/stdc++.h>
//#include <atcoder/modint>

using namespace std;
//using namespace atcoder;
using ll = long long;
//using mint = modint998244353;

int main(){
    cin.tie(nullptr);
    ios_base::sync_with_stdio(false);

    ll N, T, K, x, c=0, ans=0;
    cin >> N >> T;
    vector<ll> t(N);
    for (int i=1; i<=N-1; i++) cin >> t[i];
    cin >> K;
    vector<bool> ok(N);
    for (int i=0; i<K; i++){
        cin >> x;
        ok[x] = 1;
    }

    for (int i=1; i<=N-1; i++){
        if (ok[i]) c++;
        T -= t[i];
        if (T <= 0){
            x = (-T+10-1)/10;
            if (x > c){
                cout << -1 << endl;
                return 0;
            }
            T += 10 * x;
            c -= x;
            ans += x;
            if (T == 0){
                if (c == 0){
                    cout << -1 << endl;
                    return 0;
                }
                T += 10;
                c--;
                ans++;
            }
        }
    }

    cout << ans << endl;

    return 0;
}