#include <bits/stdc++.h>
#include <atcoder/modint>
using namespace std;
using namespace atcoder;
using mint = modint998244353;
//using mint = modint1000000007;
using ll = long long;
using ld = long double;
using pll = pair<ll, ll>;
using tlll = tuple<ll, ll, ll>;
constexpr ll INF = 1LL << 60;
template<class T> bool chmin(T& a, T b) {if (a > b) {a = b; return true;} return false;}
template<class T> bool chmax(T& a, T b) {if (a < b) {a = b; return true;} return false;}
ll safemod(ll A, ll M) {return (A % M + M) % M;}
ll divfloor(ll A, ll B) {if (B < 0) {return divfloor(-A, -B);} return (A - safemod(A, B)) / B;}
ll divceil(ll A, ll B) {if (B < 0) {return divceil(-A, -B);} return divfloor(A + B - 1, B);}
#define FINALANS(A) do {cout << (A) << '\n'; exit(0);} while (false)

int main()
{
  ll N;
  cin >> N;
  vector<ll> B(N);
  for (ll i = 0; i < N; i++)
  {
    cin >> B.at(i);
  }

  ll K = count(B.begin(), B.end(), -1);

  if (N % 2 == 1)
  {
    if (B.front() != -1 && B.back() != -1)
      cout << ((B.front() ^ B.back()) == 1 ? 1 : 0) << endl;
    else
      cout << mint(2).pow(K - 1).val() << endl;
  }
  else
  {
    cout << mint(2).pow(K - 1).val() << endl;
  }
}