#include <bits/stdc++.h>
using namespace std;
using Int = long long;
template <class T> inline bool setmin(T &A, T B){
	if (A > B){
		A = B;
		return true;
	} else {
		return false;
	}
}
template <class T> inline bool setmax(T &A, T B){
	if (A < B){
		A = B;
		return true;
	} else {
		return false;
	}
}
#define REP(x, y) for (int x = 0; x < int(y); ++x)
#define rep(x, y, z) for (int x = int(y); x < int(z); ++x)
#define PER(x, y) for (int x = int(y) - 1; x >= 0; --x)
#define per(x, y, z) for (int x = int(z) - 1; x >= int(y); --x)

void solve(){
	int N, T;
	cin >> N >> T;
	vector<int> t(N - 1);
	REP(i, N - 1){
		cin >> t[i];
	}
	int K;
	cin >> K;
	vector<bool> x(N);
	REP(i, K){
		int xx;
		cin >> xx;
		x[--xx] = true;
	}
	int ans = 0;
	int cnt = 0;
	REP(i, N - 1){
		T -= t[i];
		if (T <= 0){
			int need = -T / 10 + 1;
			if (cnt < need){
				cout << -1 << '\n';
				return;
			}
			T += need * 10;
			ans += need;
			cnt -= need;
		}
		if (x[i + 1]){
			++cnt;
		}
	}
	cout << ans << '\n';
}

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