mod = 10**9+7
n = int(input())
A = list(map(int,input().split()))

prod = [1,4,3**6]

ans = 1
for a in A:
    if a == 0:
        print(-1)
        exit()
    if a >= 4:
        print(mod)
        exit()
    ans *= prod[a-1]
    if ans > mod:
        print(mod)
        exit()
    
print(mod%ans)