mod = 998244353
n = int(input())
c = list(map(int, input().split()))
if n == 1:
    print(1)
    exit()
if c[-1] <= 0 or 0 <= c[0]:
    print(pow(2, n - 1, mod))
elif 0 in c:
    print(2 * pow(2, n - 3, mod) * 3 % mod)
else:
    print(2 * pow(2, n - 2, mod))