N, T = map(int, input().split()) ts = list(map(int, input().split())) K = int(input()) xs = list(map(lambda x: int(x)-1, input().split())) def solve(): s = set(xs) time = T cnt = 0 for i, t in enumerate(ts, 1): # print(f'{i=} {t=} {time=} {cnt=}') if t >= time + cnt * 10: return -1 if t >= time: d, m = divmod(t, 10) cnt -= d time += d * 10 if t >= time: assert cnt > 0 time += 10 cnt -= 1 assert t < time time -= t if i in s: cnt += 1 return len(s) - cnt ans = solve() print(ans)