#[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 1..n {
        let mut flg = false;
        if let Ok(_) = x.binary_search(&i) {
            flg = true;
        }
        if t > tm[i] - tm[i - 1] {
            if t <= tm[n - 1] - tm[i - 1] && flg {
                t += 10;
                cnt += 1;
            }
        } else if flg {
            t += 10;
            cnt += 1;
        } else {
            println!("-1");
            return;
        }
        t -= tm[i] - tm[i - 1];
    }
    println!("{}", cnt)
}