mod = 998244353
n,*B = map(int,open(0).read().split())
x,y = 1,0
for k,b in enumerate(B):
    s = t = 0
    if b != 0:
        s,t = (s+x)%mod,(y+t)%mod
        if n-1&k == k:
            s,t = t,s
    if b != 1:
        s,t = (s+x)%mod,(y+t)%mod
    x,y = s,t
print(y)