#include <bits/stdc++.h>
using namespace std;

int main() {
    ios::sync_with_stdio(false);
    cin.tie(nullptr);
    int N, T;
    cin >> N >> T;
    vector<int> t(N);
    for (int i = 1; i < N; i++) cin >> t[i];
    int K;
    cin >> K;
    vector<bool> f(N);
    while (K--) {
        int x;
        cin >> x;
        f[x - 1] = true;
    }
    int cnt = 0, ans = 0;
    for (int i = 1; i < N; i++) {
        if (T > t[i]) {
            T -= t[i];
        } else {
            int need = (t[i] - T + 10) / 10;
            if (need > cnt) {
                cout << -1 << endl;
                return 0;
            }
            cnt -= need;
            T += 10 * need;
            T -= t[i];
            ans += need;
        }
        cnt += f[i];
    }
    cout << (T > 0 ? ans : -1) << endl;
}