import sys
def main():
    input = sys.stdin.readline
    # 入力
    N, T = map(int, input().split())
    t = list(map(int, input().split()))
    K=int(input())
    bonus_nodes = set(map(int, input().split()))

    dp = {0: T}
    
    for i in range(1, N):
        ndp = {}
        cost = t[i-1]
        for used, time_left in dp.items():
            if time_left <= cost:
                continue
            rem = time_left - cost
            if rem > ndp.get(used, -1):
                ndp[used] = rem
            if (i+1) in bonus_nodes and rem >= 1:
                new_used = used + 1
                new_time = rem + 10
                if new_time > ndp.get(new_used, -1):
                    ndp[new_used] = new_time
        dp = ndp
        if not dp:
            print("-1")
            return
    ans = None
    for used, time_left in dp.items():
        if time_left > 0:
            if ans is None or used < ans:
                ans = used
    if ans is None:
        print("-1")
    else:
        print(ans)

if __name__ == '__main__':
    main()