#include <bits/stdc++.h>
using namespace std;
using ll = long long;
#define rep(i, n) for (int i = 0; i < (int)(n); i++)

void solve() {
  ll n, T;
  cin >> n >> T;
  vector<ll> t(n, 0);
  rep(i, n - 1) cin >> t[i + 1];
  vector<bool> x(n, false);
  {
    ll k;
    cin >> k;
    rep(i, k) {
      ll a;
      cin >> a;
      x[a - 1] = true;
    }
  }
  ll ans = 0, c = 0;
  rep(i, n - 1) {
    T -= t[i + 1];
    if (T <= 0) {
      ll r = (abs(T) + 9) / 10;
      if (T % 10 == 0)
        r++;
      ans += r;
      T += r * 10;
      c -= r;
    }
    if (c < 0) {
      cout << "-1\n";
      return;
    }
    if (x[i + 1])
      c++;
  }
  cout << ans << '\n';
}

int main() {
  std::cin.tie(nullptr);
  std::ios_base::sync_with_stdio(false);
  int T = 1;
  for (int t = 0; t < T; t++) {
    solve();
  }
  return 0;
}