MOD = 998244353
n = int(input())
a = list(map(int, input().split()))
dp = [[1, 0], [0, 0]] # [abs is 2][sig is neg]
ans = 0
for z, x in enumerate(a):
    ndp = [[0, 0], [0, 0]]
    if x == 2:
        ndp[1][0] = dp[0][0]
        ndp[1][1] = dp[0][1]
    elif x == -2:
        ndp[1][0] = dp[0][1]
        ndp[1][1] = dp[0][0]
    elif x == 1:
        for i in range(2):
            for j in range(2):
                ndp[i][j] = dp[i][j]
    elif x == -1:
        for i in range(2):
            for j in range(2):
                ndp[i][j] = dp[i][1-j]
    ans = (ans + ndp[1][1] * pow(2, max(0, n - 2 - z), MOD)) % MOD
    ndp[0][0] += pow(2, z, MOD)
    ndp[0][0] %= MOD
    dp = ndp
q = pow(2, n-1, MOD)
print(ans * pow(q, MOD-2, MOD) % MOD)