#include<iostream>
#include<string>
#include<iomanip>
#include<cmath>
#include<vector>
#include<algorithm>
#include<utility>

using namespace std;

#define int long long
#define endl "\n"

constexpr long long INF = (long long)1e18;
constexpr long long MOD = 998244353; 

struct fast_io {
	fast_io(){
		std::cin.tie(nullptr);
		std::ios::sync_with_stdio(false);
	};
} fio;

long long power(long long x, long long n){
	long long ans = 1;
	n--;
	
	for(;n > 0;n >>= 1, x *= x, ans %= MOD, x %= MOD)
		if(n&1)ans*=x;
	return ans % MOD;
}

long long power2(long long x, long long n){
	long long ans = 1;
	
	for(;n > 0;n >>= 1, x *= x, ans %= MOD, x %= MOD)
		if(n&1)ans*=x;
	return ans % MOD;
}

signed main(){
	cout<<fixed<<setprecision(10);
	
	int N;
	vector<int> a;
	int ans = 0;
	
	cin>>N;
	
	a.resize(N);
	
	for(int i = 0; i < N; i++){
		cin>>a[i];
	}
	
	for(int i = 0; i < N; i++){
		if(abs(a[i]) != 2) continue;
		int con0[2] = {0,power(2,i)};
		int con1[2] = {0,power(2,N-i-1)};		
		
		for(int j = i+1, now = 1; j < N; j++){
			if(abs(a[j]) != 1) break;;
			now *= a[j];
			
			if(now == -1) {
				con1[0] += power(2, N-j-1);
				con1[0] %= MOD;
			} else {
				con1[1] += power(2, N-j-1);
				con1[1] %= MOD;
				
			}
		}
		
		for(int j = i-1, now = 1; j >= 0; j--){
			if(abs(a[j]) != 1) break;
			now *= a[j];
			
			if(now == -1) {
				con0[0] += power(2, j);
				con0[0] %= MOD;
			} else {
				con0[1] += power(2, j);
				con0[1] %= MOD;
			}
		}
		
		if(a[i] == -2) {
			ans += con1[0] * con0[0];
			ans += con1[1] * con0[1];
			ans %= MOD;
		} else if(a[i] == 2) {
			ans += con1[0] * con0[1];
			ans += con1[1] * con0[0];
			ans %= MOD;
		}
	}
	
	ans *= power2(power2(2, N-1), MOD-2);
	ans %= MOD;
	
	cout<<ans<<endl;
	
	return 0;
}