#include <bits/stdc++.h>
#include <atcoder/all>
using namespace std;
using namespace atcoder;
using ll = long long;
using ld = long double;
using ull = unsigned long long;
using Graph = vector<vector<int>>;
#define rep(i, n) for (int i = 0; i < (int)(n); i++)
#define all(v) (v).begin(), (v).end()
#define rall(v) (v).rbegin(), (v).rend()
#define NP next_permutation
const int INF32 = 2e9;
const ll INF64 = 2e18;
const ll mod = 998244353;
// const ll mod = 1e9 + 7;
template<typename T> bool chmin(T &a, T b){if(a > b){a = b; return true;} return false;}
template<typename T> bool chmax(T &a, T b){if(a < b){a = b; return true;} return false;}
 
void cincout() {
    ios::sync_with_stdio(false);
    cin.tie(nullptr);
    cout << fixed << setprecision(15);
}
 
int main() {
    cincout();
 
    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], x[i]--;

    int ans = 0, j = 0, watch = 0;
    for (int i = 0; i < N - 1; i++) { //i, i + 1
        T -= t[i];
        if (T <= 0) {
            int need = (10 - T) / 10;
            if (need <= watch) {
                T += need * 10;
                watch -= need;
                ans += need;
            }

            else {
                ans = -1;
                break;
            }
        }   

        if (j < K && i + 1 == x[j]) {
            watch++;
            j++;
        }
    }

    cout << ans << endl;
}