use proconio::{input, marker::Usize1};

fn main() {
    input! {
        n: usize, mut remain: i64,
        t: [i64; n - 1],
        k: usize,
        x: [Usize1; k]
    }

    let mut j = 0;
    let mut n_bonus = 0;
    for (i, &t) in t.iter().enumerate() {
        if remain + n_bonus * 10 <= t {
            println!("-1");
            return;
        }
        remain -= t;

        if j < k && x[j] == i + 1 {
            j += 1;
            n_bonus += 1;
        }
    }

    let ans = ((-remain).max(-1)).div_euclid(10) + 1;
    println!("{}", ans);
}