N,T=map(int,input().split())
t=list(map(int,input().split()))
K=int(input())
x=set(map(int,input().split()))
dp=[[] for _ in range(N)]
dp[0]=[(0,T)]
for i in range(N-1):
    for cnt,rest in dp[i]:
        if rest-t[i]>0:
            dp[i+1].append((cnt,rest-t[i]))
            if i in x:
                dp[i+1].append((cnt+1,rest-t[i]+10))
if len(dp[N-1]):
    dp[N-1].sort()
    print(dp[N-1][0][0])
else:
    print(-1)