import sys
input = lambda : sys.stdin.readline().rstrip()
sys.setrecursionlimit(max(1000, 10**9))
write = lambda x: sys.stdout.write(x+"\n")


n = int(input())
a = list(map(int, input().split()))
ls = []
from collections import deque
l = deque()
flg = False
left = True
first = True
right = False
seen0 = False
for num in a:
    if num==0:
        if l:
            if flg:
                if first and seen0:
                    left = False
                first = False
                ls.append(list(l))
            l = deque()
            flg = False
        seen0 = True
    elif (num==2 or num==-2) and flg:
        ls.append(list(l))
        if seen0 and first:
            left = False
            first = False
        while abs(l[0])!=2:
            l.popleft()
        l.popleft()
        l.append(num)
        flg = True
    elif (num==2 or num==-2):
        l.append(num)
        flg = True
    else:
        l.append(num)
if l and flg:
    if seen0 and first:
        left = False
    ls.append(list(l))
    right = True
M = 998244353
inv2 = pow(2, M-2, M)
invs = [None]*(n+10)
invs[0] = 1
for i in range(1, n+10):
    invs[i] = invs[i-1]*inv2
    invs[i] %= M
def sub(l, left=False, right=False):
    if 2 in l:
        ind = l.index(2)
        flg2 = True
    else:
        ind = l.index(-2)
        flg2 = False
    e0 = inv2 if (ind>0 or not left) else 1
    o0 = 0
    e1 = inv2 if (ind<len(l)-1 or not right) else 1
    o1 = 0
    even = True
    for i in range(ind):
        if l[ind-i-1]==-1:
            even = not even
        tmp = invs[i+2] if (i<ind-1 or (not left)) else invs[i+1]
        if even:
            e0 += tmp
        else:
            o0 += tmp
    even = True
    for i in range(len(l)-ind-1):
        if l[ind+i+1]==-1:
            even = not even
        tmp = invs[i+2] if (i<len(l)-ind-2 or (not right)) else invs[i+1]
        if even:
            e1 += tmp
        else:
            o1 += tmp
    if not flg2:
        ans = e0*e1 + o0*o1
    else:
        ans = e0*o1 + e1*o0
#     print(left, right, e0, e1, o0, o1, ans%M)
    return ans%M
if len(ls)==0:
    ans = 0
elif len(ls)==1:
    ans = sub(ls[0], left=left, right=right)
else:
    ans = 0
    ans += sub(ls[0], left=left)
    ans %= M
    for i in range(1, len(ls)-1):
        ans += sub(ls[i])
        ans %= M
    ans += sub(ls[-1], right=right)
    ans %= M
print(ans%M)