#include <bits/stdc++.h>

using namespace std;

int main() {
    int n, t;
    cin >> n >> t;
    int t2[n];
    for (int i = 0; i < n-1; i++) {
        cin >> t2[i];
    }
    int k;
    cin >> k;
    int x[k];
    set<int> xs;
    for (int i = 0; i < k; i++) {
        cin >> x[i];
        xs.insert(x[i]-2);
    }

    int memo = t;
    int memo2[n-1];
    for (int i = 0; i < n-1; i++) {
        memo -= t2[i];
        if (memo <= 0) {
            puts("-1");
            return 0;
        }
        if (xs.contains(i)) {
            memo += 10;
        }
        memo2[i] = memo;
    }

    int min_v = memo;
    int cnt = 0;
    for (int i = n-2; i >= 0; i--) {
        if (xs.contains(i)) {
            if (min_v-10 <= 0 || memo2[i]-10 <= 0) {
                break;
            }
            min_v = min(min_v-10, memo2[i]-10);
            cnt++;
        }
    }

    cout << k-cnt << endl;

    return 0;
}