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

#define For(i, a, b) for(int i = (a); i < (b); i++)
#define rep(i, n) For(i, 0, n)
#define rFor(i, a, b) for(int i = (a); i >= (b); i--)
#define ALL(v) (v).begin(), (v).end()
#define rALL(v) (v).rbegin(), (v).rend()

using lint = long long;
using ld = long double;

int INF = 2000000000;
lint LINF = 1000000000000000000;

struct SetupIo {
    SetupIo() {
        ios::sync_with_stdio(false);
        cin.tie(nullptr);
        cout << fixed << setprecision(15);
    }
} setupio;

int main() {
    int N, T;
    cin >> N >> T;
    vector<int> t(N - 1);
    rep(i, N - 1) {
        cin >> t[i];
    }
    int K;
    cin >> K;
    vector<bool> can(N, false);
    rep(i, K) {
        int x;
        cin >> x;
        x--;
        can[x] = true;
    }
    int sum = accumulate(ALL(t), 0);
    int need = max(0, (sum - T) / 10 + 1);
    int used = 0;
    rep(i, N - 1) {
        if (can[i] && used < need) {
            T += 10;
            used++;
        }
        T -= t[i];
        if (T <= 0) {
            cout << -1 << "\n";
            return 0;
        }
    }
    cout << need << "\n";
}