#include <cstdio>
#include <cstring>
#include <iostream>
#include <string>
#include <cmath>
#include <bitset>
#include <vector>
#include <map>
#include <set>
#include <queue>
#include <deque>
#include <algorithm>
#include <complex>
#include <unordered_map>
#include <unordered_set>
#include <random>
#include <cassert>
#include <fstream>
#include <utility>
#include <functional>
#include <time.h>
#include <stack>
#include <array>
#define popcount __builtin_popcount
using namespace std;
using ll=long long;
typedef pair<int, int> P;
const ll MOD=998244353;
ll powmod(ll a, ll k){
    ll ap=a, ans=1;
    while(k){
        if(k&1){
            ans*=ap;
            ans%=MOD;
        }
        ap=ap*ap;
        ap%=MOD;
        k>>=1;
    }
    return ans;
}
ll inv(ll a){
    return powmod(a, MOD-2);
}
int main()
{
    int n; cin>>n;
    int a[200020];
    for(int i=0; i<n; i++) cin>>a[i];
    ll ans=0;
    for(int i=0; i<n; i++){
        if(abs(a[i])!=2) continue;
        int l=i-1, r=i+1;
        while(l>=0){
            if(abs(a[l])!=1) break;
            l--;
        }
        while(r<n){
            if(abs(a[r])!=1) break;
            r++;
        }
        ll sl[2]={}, sr[2]={};
        int p=0;
        for(int j=i; j>l; j--){
            if(j<i && a[j]==-1) p^=1;
            (sl[p]+=powmod(2, max(0, j-1)))%=MOD;
        }
        p=0;
        for(int j=i+1; j<=r; j++){
            if(j-1>i && a[j-1]==-1) p^=1;
            (sr[p]+=powmod(2, MOD-1-min(n-1, j)))%=MOD;
        }
        int p0=0;
        if(a[i]==-2) p0^=1;
        for(int p=0; p<2; p++){
            for(int q=0; q<2; q++){
                if(p^q^p0){
                    (ans+=sl[p]*sr[q])%=MOD;
                }
            }
        }
      //cout<<ans<<endl;
    }
    cout<<ans<<endl;
    return 0;
}