import std;

void main () {
    int N, T; readln.read(N, T);
    auto t = readln.split.to!(int[]);
    int K = readln.chomp.to!int;
    auto x = readln.split.to!(int[]);

    // 貪欲に前からとってよい
    int tsum = sum(t);
    int need = (max(tsum + 1 - T, 0) + 10 - 1) / 10;
    int ans = need;

    bool[int] mp;
    foreach (v; x) mp[v] = true;

    bool ok = true;
    int cur = T;
    foreach (i; 0 .. N - 1) {
        if (cur - t[i] <= 0) ok = false;
        cur -= t[i];

        if (i + 2 in mp) {
            if (0 < need) {
                need--;
                cur += 10;
            }
        }
    }

    if (ok) {
        writeln(ans);
    }
    else {
        writeln(-1);
    }
}

void read (T...) (string S, ref T args) {
    import std.conv : to;
    import std.array : split;
    auto buf = S.split;
    foreach (i, ref arg; args) {
        arg = buf[i].to!(typeof(arg));
    }
}