#[allow(unused_imports)]
use std::{
    cell::RefCell, convert::{Infallible, TryFrom, TryInto as _},
    fmt::{self, Debug, Display, Formatter,}, fs::{File}, hash::{Hash, Hasher},
    iter::{Product, Sum}, marker::PhantomData,
    ops::{Add, AddAssign, Sub, SubAssign, Div, DivAssign, Mul, MulAssign, Neg, RangeBounds},
    str::{FromStr, SplitWhitespace}, sync::{atomic::{self, AtomicU32, AtomicU64}, Once},
    collections::{*, btree_map::Range}, mem::{swap},
    cmp::{self, Reverse, Ordering, Eq, PartialEq, PartialOrd},
    thread::LocalKey, f64::consts::PI, time::Instant, rc::Rc,
    ptr::null_mut,
    io::{self, stdin, Read, read_to_string, BufWriter, BufReader, stdout, Write},
};
#[allow(unused_imports)]
use proconio::{input, input_interactive, marker::{*}};
#[allow(unused_imports)]
//use rand::{thread_rng, Rng, seq::SliceRandom};
#[allow(unused_imports)]
//use ac_library::{*};

#[allow(dead_code)]
const INF: i64 = 1<<61;
#[allow(dead_code)]
const MOD: i64 = 998244353;
#[allow(dead_code)]
const D: [(usize, usize); 4] = [(1, 0), (0, 1), (!0, 0), (0, !0)];

//use proconio::fastout;
//#[fastout]
fn main() {
    input! {
        n: usize, mut t: i64,
        s: [i64; n-1],
        k: usize,
        x: [Usize1; k]
    }
    let mut add = vec![0; n];
    for &v in &x{
        add[v] += 1;
    }
    let mut rest = 0;
    let mut ans = 0;
    for i in 0..n-1{
        t -= s[i];
        while t <= 0 && rest > 0{
            rest -= 1;
            ans += 1;
            t += 10;
        }
        if t <= 0{
            println!("-1");
            return;
        }
        rest += add[i+1];
    }
    println!("{}", ans);
}