#include <bits/stdc++.h>

using namespace std;

#define all(v) v.begin(),v.end()
#define resort(v) sort(v.rbegin(),v.rend())
using ll = long long;
using ull = unsigned long long;
using vll=vector<ll>;
using vvll = vector<vector<ll>>;
using P = pair<ll,ll>;
using vp=vector<pair<ll, ll>>;
using djks=priority_queue<P, vp, greater<P>>;

const ll inf=1ll<<60;
#define mod10 (ll)1e9+7
#define mod99 (ll)998244353
const double PI = acos(-1);

#define rep(i,n) for (ll i=0;i<n;++i)
#define per(i,n) for(ll i=n-1;i>=0;--i)
#define rep2(i,a,n) for (ll i=a;i<n;++i)
#define per2(i,a,n) for (ll i=n-1;i>=a;--i)


template<class T>bool chmax(T &a, const T &b) { if (a<b) { a=b; return true; } return false; }
template<class T>bool chmin(T &a, const T &b) { if (b<a) { a=b; return true; } return false; }

ll dx[] = {1, 0, -1, 0, -1, 1, -1, 1};
ll dy[] = {0, 1, 0, -1, -1, 1, 1, -1};

void solve() {
    ll n, t; cin >> n >> t;
    vll ts(n-1); rep(i,n-1)cin>>ts[i];
    ll k; cin >> k;
    vll xs(n, 0); rep(i, k) {
        ll val; cin >> val;
        xs[val-1]=1;
    }

    ll used = 0;
    ll stock = 0;
    ll time = 0;
    rep(i, n-1) {
        time += ts[i];
        while(t<=time) {
            if(stock==0) {
                cout << "-1\n";
                return;
            }
            stock--;
            used++;
            t += 10;
        }

        stock+=xs[i+1];
    }
    cout << used << '\n';
}

int main() {
    cin.tie(0);
    ios::sync_with_stdio(false);
    int t=1;
    //cin >> t;
    while(t--)solve();
}