#[allow(unused)]
use proconio::{input, marker::Chars};

fn main() {
    input! {
        n: usize,
        mut t: i32,
        mut tm: [i32; n - 1],
        k: usize,
        x: [usize; k],
    }
    tm.insert(0, 0);
    for i in 1..n {
        tm[i] += tm[i - 1];
    }
    let mut cnt = 0;
    for i in 0..n - 1 {
        if t > tm[i + 1] - tm[i] {
            t -= tm[i + 1] - tm[i];
            if t <= tm[n - 1] - tm[i + 1] {
                if let Ok(_) = x.binary_search(&(i + 1)) {
                    t += 10;
                    cnt += 1;
                }
            }
        } else {
            println!("-1");
            return;
        }
    }
    println!("{}", cnt)
}