#include <iostream>
#include <string>
#include <cstdlib>
#include <cmath>
#include <vector>
#include <unordered_map>
#include <map>
#include <set>
#include <algorithm>
#include <queue>
#include <stack>
#include <functional>
#include <bitset>
#include <assert.h>
#include <unordered_map>
#include <fstream>
#include <ctime>
#include <complex>
using namespace std;
typedef long long ll;
typedef vector<ll> vl;
typedef vector<vl> vvl;
typedef vector<char> vc;
typedef vector<string> vs;
typedef vector<bool> vb;
typedef vector<double> vd;
typedef pair<ll,ll> P;
typedef pair<int,int> pii;
typedef vector<P> vpl;
typedef tuple<ll,ll,ll> tapu;
#define rep(i,n) for(int i=0; i<(n); i++)
#define REP(i,a,b) for(int i=(a); i<(b); i++)
#define all(x) (x).begin(), (x).end()
#define rall(x) (x).rbegin(), (x).rend()
const int inf = 1<<30;
const ll linf = 1LL<<62;
const int MAX = 2020000;
ll dy[8] = {1,-1,0,0,1,-1,1,-1};
ll dx[8] = {0,0,1,-1,1,-1,-1,1};
const double pi = acos(-1);
const double eps = 1e-7;
template<typename T1,typename T2> inline bool chmin(T1 &a,T2 b){
	if(a>b){
		a = b; return true;
	}
	else return false;
}
template<typename T1,typename T2> inline bool chmax(T1 &a,T2 b){
	if(a<b){
		a = b; return true;
	}
	else return false;
}
template<typename T> inline void print(T &a){
    for(auto itr = a.begin(); itr != a.end(); itr++){
		cout << *itr << " ";
	}
    cout << "\n";
}
template<typename T1,typename T2> inline void print2(T1 a, T2 b){
	cout << "debug: " << a << " " << b << "\n";
}
template<typename T1,typename T2,typename T3> inline void print3(T1 a, T2 b, T3 c){
	cout << "debug: " << a << " " << b << " " << c << "\n";
}
void mark() {cout << "#" << "\n";}
ll pcount(ll x) {return __builtin_popcountll(x);}
//const int mod = 1e9 + 7;
const int mod = 998244353;

template <std::uint_fast64_t Modulus> class modint {
  using u64 = std::uint_fast64_t;

public:
  u64 a;

  constexpr modint(const u64 x = 0) noexcept : a(x % Modulus) {}
  constexpr u64 &value() noexcept { return a; }
  constexpr const u64 &value() const noexcept { return a; }
  constexpr modint operator+(const modint rhs) const noexcept {
	return modint(*this) += rhs;
  }
  constexpr modint operator-(const modint rhs) const noexcept {
	return modint(*this) -= rhs;
  }
  constexpr modint operator*(const modint rhs) const noexcept {
	return modint(*this) *= rhs;
  }
  constexpr modint operator/(const modint rhs) const noexcept {
	return modint(*this) /= rhs;
  }
  constexpr modint &operator+=(const modint rhs) noexcept {
	a += rhs.a;
	if (a >= Modulus) {
	  a -= Modulus;
	}
	return *this;
  }
  constexpr modint &operator-=(const modint rhs) noexcept {
	if (a < rhs.a) {
	  a += Modulus;
	}
	a -= rhs.a;
	return *this;
  }
  constexpr modint &operator*=(const modint rhs) noexcept {
	a = a * rhs.a % Modulus;
	return *this;
  }
  constexpr modint &operator/=(modint rhs) noexcept {
	u64 exp = Modulus - 2;
	while (exp) {
	  if (exp % 2) {
		*this *= rhs;
	  }
	  rhs *= rhs;
	  exp /= 2;
	}
	return *this;
  }
};

using mint = modint<mod>;

ll modpow(ll x, ll n, ll mod){
	ll res = 1;
	while(n > 0){
		if(n & 1) res = res * x % mod;
		x = x * x % mod;
		n >>= 1;
	}
	return res;
}

template<typename T> struct BIT{
	vector<T> dat;
	ll sz;
	//all 1-indexed
	BIT(ll sz) : sz(sz){
		dat.assign(++sz, 0);
	}

	T sum(ll k){
		T ret = 0;
		for(++k; k > 0; k -= k & -k) ret += dat[k];
		return (ret);
	}

	void add(ll k, T x){
		for(++k; k < dat.size(); k += k & -k) dat[k] += x;
	}
	
	ll get(T k){
		if(k <= 0) return 0; 
		ll ret = 0;
		int n = 1; while(n < sz) n *= 2;
		for(int i=n/2; i>0; i/=2){
			if(ret+i < sz && dat[ret+i] < k){
				k -= dat[ret+i];
				ret += i;
			}
		}
		return ret;
	}
};

int main(){
	int n; cin >> n;
	vl a(n); rep(i,n) cin >> a[i];
	vl nxt(n,n);
	for(int i=n-1; i>=1; i--){
		nxt[i-1] = nxt[i];
		if(abs(a[i]) == 2 || a[i] == 0) nxt[i-1] = i;
	}
	mint p = 0, q = modpow(2,n-1,mod);
	BIT<mint> m(n), M(n);
	bool plus = true;
	rep(i,n){
		if(a[i] < 0) plus = !plus;
		if(plus) M.add(i,modpow(2,n-i-2,mod));
		else m.add(i,modpow(2,n-i-2,mod));
	}
	plus = true;
	rep(i,n){
		if(a[i] == 0) continue;
		int l,r;
		if(abs(a[i]) == 2){
			l = i;
			r = nxt[i];
		}else{
			l = nxt[i];
			r = nxt[l];
		}
		if(l == n) break;
		if(plus) p += (m.sum(r-1) - m.sum(l-1)) * modpow(2,i-1,mod);
		else p += (M.sum(r-1) - M.sum(l-1)) * modpow(2,i-1,mod);
		if(a[i] < 0) plus = !plus;
	}
	cout << (p / q).value() << "\n";
}