from itertools import *
from collections import *
n = int(input())
e = [int(input()) for _ in range(n)]
zero = {(0,0,0),(1,0,0),(1,1,1)}
one = set(product(range(2), repeat=3)) - zero
table = [zero, one]
result = 0
for start_left, start_middle, start_right in table[e[0]]:
    state = Counter()
    state[start_middle, start_right] = 1
    for bit in e[1:-1]:
        temp = Counter()
        for left, middle, right in table[bit]:
            temp[middle, right] += state[left, middle]
            temp[middle, right] %= 10**9+7
        state = temp
    for (left, middle), count in state.items():
        if (middle == start_left
                and (left, middle, start_middle) in table[e[-1]]):
            result += count
            result %= 10**9+7
print(result)