#!/usr/bin/env python3
# %%
import sys
read = sys.stdin.buffer.read
readline = sys.stdin.buffer.readline
readlines = sys.stdin.buffer.readlines


MOD = 10**9 + 7
# %%
N, *B = map(int, read().split())


# %%
def solve(B, end, start):
    dp = [0, 0, 0, 0]
    dp[2 * end + start] = 1
    for x in B:
        newdp = [0, 0, 0, 0]
        if x == 0:
            newdp[0] += dp[0]
            newdp[0] += dp[2]
            newdp[3] += dp[3]
        elif x == 1:
            newdp[1] += dp[0]
            newdp[2] += dp[1]
            newdp[3] += dp[1]
            newdp[1] += dp[2]
            newdp[2] += dp[3]
        dp = [x % MOD for x in newdp]
    return dp[2 * end + start]


# %%
answer = sum(solve(B, i, j) for i in [0, 1] for j in [0, 1])
answer %= MOD
print(answer)