#include <algorithm>
#include <iostream>
#include <vector>
using namespace std;

int main() {
    int N, T;
    cin >> N >> T;
    vector<int> t(N - 1);
    for (int i = 0; i < N - 1; i++) {
        cin >> t[i];
    }
    int K;
    cin >> K;
    vector<int> x(K);
    for (int i = 0; i < K; i++) {
        cin >> x[i];
    }
    vector<bool> has_clock(N, false);
    for (int i = 0; i < K; i++) {
        has_clock[x[i] - 1] = true;
    }

    if (N > 3000) {
        return 0;
    }
    int INF = 1000000002;
    vector<vector<int>> dp(N, vector<int>(N, -INF));
    dp[0][0] = T;
    for (int i = 0; i < N - 1; i++) {
        for (int j = 0; j <= i; j++) {
            if (dp[i][j] <= 0) {
                continue;
            }
            if (has_clock[i + 1]) {
                dp[i + 1][j + 1] = max(dp[i + 1][j + 1], dp[i][j] + 10 - t[i]);
            }
            dp[i + 1][j] = max(dp[i + 1][j], dp[i][j] - t[i]);
        }
    }
    int ans = INF;
    for (int i = 0; i <= N - 1; i++) {
        if (dp[N - 1][i] > 0) {
            ans = min(ans, i);
        }
    }
    if (ans > N) {
        cout << -1 << endl;
        return 0;
    }
    cout << ans << endl;
}