MOD = 1000000007

def main():
    _n = int(input())
    a = [int(x) for x in input().split()]
    res = 1
    for v in a:
        if 1 <= v <= 3:
            for x in range(1, v**v):
                res *= x
                res %= MOD
        else:
            print("0")
            return
    print(res)



if __name__ == "__main__":
    main()