use proconio::input;
use std::collections::HashSet;

fn main() {
    input!{
        N:usize, T:usize,
        mut t:[usize;N-1],
        K:usize,
        x:[usize;K]
    }

    t.insert(0,0);
    t.insert(1,0);
    let x:HashSet<usize> = HashSet::from_iter(x.iter().cloned());

    let mut cnt:isize = T.clone() as isize;
    let mut useble_clock:usize = 0;
    let mut ans:isize = 0;
    for i in 2..=N {
        // 地点iに行けるか否かの判定
        
        cnt -= t[i] as isize;
        if cnt <= 0 {
            if (-cnt)/10 + 1 > (useble_clock as isize) {
                ans = -1;
                break;
            } else {
                let use_clock:usize = (-cnt as usize)/10 + 1;
                useble_clock -= use_clock as usize;
                ans += use_clock as isize;
                cnt += 10*(use_clock as isize);
            }
        }
        if x.contains(&i) && cnt>0 {
            useble_clock += 1;
        }
    }
    println!("{}", ans);
}