#include <bits/stdc++.h>

#include <atcoder/all>
using namespace std;
using i32 = int;
using u32 = unsigned int;
using i64 = long long;
using u64 = unsigned long long;
#define FAST_IO                \
  ios::sync_with_stdio(false); \
  cin.tie(0);
const i64 INF = 1001001001001001001;
using Modint = atcoder::static_modint<998244353>;

int main() {
  FAST_IO
  auto ans = 0LL;

  int N,T;
  cin >> N >> T;
  vector<i64> t(N-1);
  for (auto& x : t) cin >> x;

  int K;
  cin >> K;
  vector<int> x(K);
  for (auto& y : x) cin >> y;


  vector<bool> x2(N);
  for (int i = 0; i < K; i ++) {
    x2[x[i]-1] = true;
  }

  i64 tm = 0;
  for (int i = 0; i < N-1; i ++) {
    if (T + tm * 10 <= t[i]) {
      ans = -1;
      break;
    }
    T -= t[i];
    if (T <= 0) {
      auto t = abs(T) / 10 + 1;
      T += t * 10;
      tm -= t;
      ans += t;
    }
    if (x2[i+1]) {
      tm ++;
    }
  }


  cout << ans << endl;
}