# coding: utf-8
# Your code here!
N=int(input())
A=list(map(int,input().split()))

ans=1
mod=(10**9+7)
for a in A:
    if a>=4:
        ans*=(mod+1)
    elif a==3:
        ans*=3**6
    elif a==2:
        ans*=2**2
    elif a==0:
        ans*=0
    
    if ans>mod:
        print(mod)
        exit()

if ans==0:
    print(-1)
else:
    print(mod%ans)