#define _USE_MATH_DEFINES
#include  <cmath>
#include <cstdio>
#include <vector>
#include <iostream>
#include <algorithm>
#include <string>
#include<math.h>
#include<iomanip>
#include<stdio.h>
#include <stdlib.h>
#include<stdio.h>
#include <queue>
#include<map>
#include <fstream>
#include <sstream>
#include<set>
#include<stack>
#include<time.h>
#include <sys/types.h>
#include <tuple>
#include <numeric>
#include <iterator>

typedef long long int ll;
//#include<bits/stdc++.h>


using namespace std;

ll gcd(ll a, ll b) {
    if (a < b)swap(a, b);
    if (b == 0)return a;
    return gcd(b, a % b);
}
int lcm(int a, int b) {
    return a * b / gcd(a, b);
}


string ans,s = "";
void tec(string s,ll i) {
    if (i == 1) {
        ans = s;
        return;
    }
    
    i--;
    if (i % 2 == 0) tec(s+'A',i/2); 
    if (i % 3 == 0)  tec(s + 'B', i/3);  
}



int main()
{

    int Q;
    Q = 1;
    //cin >> Q;   

    while (Q--) {
        int n, t;
        cin >> n >> t;
        vector<int>r(n );
        r[0] = t;
        for (int i = 0; i < n-1; i++) {
            cin >> r[i];
           
        }
        deque<int>d;
        int k;
        cin >> k;
        for (int i = 0; i < k; i++) {
            int x;
            cin >> x;
            x--;
            d.push_back(x);
        }
        int a = 0;
        for (int i = 0; i < n - 1; i++) {
            if (d[a] == i) {
                t += 10; a++;
            }
            t -= r[i];
            if (t <= 0) {
                cout << -1; return 0;
            }
            
            
        }
        cout << max(0, k - (t - 1) / 10);
      
    }
        return 0;
}