mod = 998244353
N = int(input())
A = list(map(int, input().split()))
ans = 0
for i in range(1,N-1):
  if abs(A[i])==2:
    l_p = 1<<(i-1)
    l_m = 0
    cuml = 1
    for j in range(i-1,0,-1):
      if abs(A[j])!=1:
        break
      cuml *= A[j]
      if cuml == 1:
        l_p += 1<<(j-1)
      else:
        l_m += 1<<(j-1)
    r_p = 1<<(N-2-i)
    r_m = 0
    cumr = 1
    for j in range(i+1,N-1):
      if abs(A[j])!=1:
        break
      cumr *= A[j]
      if cumr == 1:
        r_p += 1<<(N-2-i)
      else:
        r_m += 1<<(N-2-i)
    if A[i]==2:
      ans += l_p * r_m + l_m * r_p
    else:
      ans += l_p * r_p + l_m * r_m
    ans %= mod
cum = 1
for i in range(N):
  cum *= A[i]
  if cum == -2:
    if i<N-1:
      ans += 1<<(N-2-i)
    else:
      ans += 1<<(N-1-i)
  if abs(cum)>2 or cum==0:
    break
cum = 1
for i in range(N-1,0,-1):
  cum *= A[i]
  if cum == -2:
    ans += 1<<(i-1)
  if abs(cum)>2 or cum==0:
    break
ans %= mod
ans *= pow(pow(2,N-1,mod),mod-2,mod)
print(ans%mod)