#include <bits/stdc++.h>
#include <unordered_map>
#include <stdlib.h>
#include <boost/multiprecision/cpp_int.hpp>
#include <atcoder/all>
using namespace atcoder;
using namespace boost::multiprecision;
using namespace std;
#define rep(i, a, n) for(ll i = a; i < n; i++)
#define rrep(i, a, n) for(ll i = a; i >= n; i--)
#define ll long long
#define pii pair<int, int>
#define pll pair<ll, ll>
#define all(x) (x).begin(), (x).end()
//constexpr ll MOD = 1000000007;
constexpr ll MOD = 998244353;
constexpr int IINF = 1001001001;
constexpr ll INF = 1LL<<60;
template<class t,class u> void chmax(t&a,u b){if(a<b)a=b;}
template<class t,class u> void chmin(t&a,u b){if(b<a)a=b;}

using mint = modint998244353;

ll gcd(ll a, ll b){
    if(a%b == 0){
      return b;
    }else{
      return gcd(b, a%b);
    }
}

ll lcm(ll a, ll b){
    return a*b / gcd(a, b);
}

ll powMod(ll x, ll n) {
    if (n == 0) return 1 % MOD;
    ll val = powMod(x, n / 2);
    val *= val;
    val %= MOD;
    if (n % 2 == 1) val *= x;
    return val % MOD;
}

int main() {
    ll n, t; cin >> n >> t;
    vector<ll> tvec(n);
    rep(i,0,n-1) cin >> tvec[i];
    ll k; cin >> k;
    vector<ll> plus(n);
    rep(i,0,k){
        ll x; cin >> x;
        x--;
        plus[x] = 1;
    }
    ll time = t, p = 0, ans = 0;
    rep(i,0,n-1){
        if(time > tvec[i]);
        else if(time+10 > tvec[i]){
            if(p >= 1)p--, ans++,  time+= 10;
            else{
                cout << -1 << endl;
                return 0;
            }
        }else if(time+20 > tvec[i]){
            if(p >= 2)p-=2, ans+=2,time+= 20;
            else{
                cout << -1 << endl;
                return 0;
            }
        }else{
            cout << -1 << endl;
            return 0;
        }
        time -= tvec[i];
        p += plus[i+1];
    }
    cout << ans << endl;
    return 0;
}