#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)

class mintcombination
{
public:
  vector<mint> fac, finv, inv;

  mintcombination(ll M)
  {
    fac.resize(M + 1);
    finv.resize(M + 1);
    inv.resize(M + 1);

    fac.at(0) = 1, finv.at(0) = 1;
    fac.at(1) = 1, finv.at(1) = 1, inv.at(1) = 1;

    for (ll i = 2; i <= M; i++)
    {
      fac.at(i) = fac.at(i - 1) * i;
      inv.at(i) = mint::mod() - inv.at(mint::mod() % i) * (mint::mod() / i);
      finv.at(i) = finv.at(i - 1) * inv.at(i);
    }
  }

  mint P(ll N, ll K)
  {
    if (N < K) return 0;
    if (N < 0 || K < 0) return 0;
    return fac.at(N) * finv.at(N - K);
  }

  mint C(ll N, ll K)
  {
    if (N < K) return 0;
    if (N < 0 || K < 0) return 0;
    return fac.at(N) * finv.at(K) * finv.at(N - K);
  }

  mint H(ll N, ll K)
  {
    return C(N + K - 1, K);
  }
};

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

  vector<ll> C;
  if (N % 2 == 1)
    C = {B.front(), B.back()};
  else
  {
    for (ll i = 0; i < N; i++)
    {
      C.at(i) = B.at(i);
    }
  }

  ll X = 0;
  for (auto c : C)
  {
    if (c != -1)
      X ^= c;
  }

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

  mintcombination com(N);

  if (K == 0)
  {
    ll X = 0;
    for (auto c : C)
    {
      X ^= c;
    }
    cout << (X == 1 ? 1 : 0) << endl;
  }
  else
  {
    mint ans = 0;
    for (ll i = X; i <= K; i += 2)
    {
      ans += com.C(K, i);
    }
    ans *= mint(2).pow(M - K);
    cout << ans.val() << endl;
  }
}