mod = 998244353
N = int(input())
A = list(map(int, input().split()))
ans = 0
dp = [0]*5
dp[1] = 1
for i in range(N):
  new_dp = [0]*5
  if i<N-1:
    new_dp[1] = pow(2,i,mod)
  else:
    new_dp[1] = pow(2,i-1,mod)
  for j in range(-2,3):
    if abs(j*A[i])<=2:
      new_dp[j*A[i]] += dp[j]
  dp = new_dp
  if i==N-1:
    ans += dp[-2]
  else:
    ans += dp[-2]*pow(2,N-2-i,mod)
  ans %= mod
ans *= pow(pow(2,N-1,mod),mod-2,mod)
print(ans%mod)