def greedy(A):
    while len(A)>1:
        B=[]
        for i in range(len(A)-1):
            B.append(A[i]^A[i+1])
        A=B
    return A[0]

def nCr_mod2(n,r):
    return 1 if n|r==n else 0
#==================================================
N=int(input())
B=list(map(int,input().split()))

F=[nCr_mod2(N-1,r) for r in range(N)]
Mod=998244353

DP=[1,0]
for i,b in enumerate(B):
    E=DP.copy()
    if b==-1:
        if F[i]==0:
            DP[0]=2*DP[0]%Mod
            DP[1]=2*DP[1]%Mod
        else:
            DP[0]=DP[1]=(DP[0]+DP[1])%Mod
    elif b==1 and F[i]==1:
        DP=E[::-1]

print(DP[1])