N = int(input())
A = list(map(int,input().split()))
mod = 998244353
inv = pow(2,mod-2,mod)

res = 0

for i in range(N):
    if abs(A[i])==2:
        base = pow(2,max(i-1,0),mod)
        left_pos = base
        left_nega = 0
        prod = 1
        if i!=1:
            base = (base * inv) % mod
        for j in range(1,i+1):
            if abs(A[i-j])==1:
                prod *= A[i-j]
                if prod>0:
                    left_pos += base
                else:
                    left_nega += base
            else:
                break
            if j!=i-1:
                base = (base * inv) % mod

        base = pow(2,max(0,N-i-2),mod)
        right_pos = base
        right_nega = 0
        prod = 1
        if i!=N-2:
            base = (base * inv) % mod
        for j in range(1,N-i):
            print(base)
            if abs(A[i+j])==1:
                prod *= A[i+j]
                if prod>0:
                    right_pos += base
                else:
                    right_nega += base
            else:
                break
            if j!=N-i-2:
                base = (base * inv) % mod

        if A[i]==2:
            res += left_pos * right_nega + left_nega * right_pos
        else:
            res += left_pos * right_pos + left_nega * right_nega
        res %= mod
        #print(left_pos,left_nega,right_pos,right_nega)

#print(res)
ans = res * pow(2,(N-1)*(mod-2),mod)
print(ans%mod)