import sys, time, random
from collections import deque, Counter, defaultdict
def debug(*x):print('debug:',*x, file=sys.stderr)
input = lambda: sys.stdin.readline().rstrip()
ii = lambda: int(input())
mi = lambda: map(int, input().split())
li = lambda: list(mi())
inf = 2 ** 61 - 1
mod = 998244353

n, t = mi()

d = li()

k = ii()

x = li()

clock = [0] * n

for i in range(k):
    clock[x[i] - 1] += 1
    
dp = [-inf] * (k + 1)

dp[0] = t

for i in range(n - 1):
    e = [-inf] * (k + 1)
    for j in range(k + 1):
        if dp[j] <= 0: continue
        e[j] = max(e[j], dp[j] - d[i])
        if j < k and clock[i]:
            e[j + 1] = max(e[j + 1], dp[j] - d[i] + 10)
            
    dp = e
ans = -1

for i in range(0, k + 1):
    if dp[i] > 0:
        ans = i
        break
    
print(ans)