import sys
ni = lambda :int(input())
na = lambda :list(map(int,input().split()))
yes = lambda :print("yes");Yes = lambda :print("Yes");YES = lambda : print("YES")
no = lambda :print("no");No = lambda :print("No");NO = lambda : print("NO")
#######################################################################


n, m = na()
a = na()
s = na()
ok = [0] * (n + 1)
for i in s:
    ok[i] = 1

ans = 0
t = list(s)
while t:
    x = t.pop()
    ans += 1
    for y in s:
        # print(x, y)
        if ok[a[x + y]] == 0:
            ok[a[x+y]] = 1
            t.append(a[x + y])

print(ans)