use proconio::input;
use std::collections::BTreeSet;
use proconio::marker::Usize1;

fn main() {
    input! {
        n: usize,
        t: usize,
        a: [usize; n - 1],
        k: usize,
        x: [Usize1; k]
    }
    let  x: BTreeSet<_> = x.into_iter().collect();
    
    if !ok(k, t, &a, &x) {
        println!("-1");
        return;
    }
    
    let mut l = -1;
    let mut r = k as isize;
    while l + 1 < r {
        let m = (l + r) as usize / 2;
        if ok(m, t, &a, &x) {
            r = m as isize;
        } else {
            l = m as isize;
        }
    }
    
    println!("{}", r);
}

fn ok(mut m:usize, t:usize, a:&Vec<usize>, x:&BTreeSet<usize>) -> bool {
    let mut now = t;
    let mut res = true;
    for i in 0..a.len() {
        res &= now > a[i];
        if !res { break }
        now -= a[i];
        if x.contains(&i) && m > 0 {
            now += 10;
            m -= 1;
        }
    }
    
    res
}