#include <bits/stdc++.h>
using namespace std;
int main(){
    int N,mod=998244353,count=0,temp,ans=mod/2+1,flg=1,B,cur=0;
    cin>>N;
    for(int i=0;i<N;++i){
        cin>>B;
        if(B==-1){
            ans=(ans<<1)%mod;
            flg&=count;
        }else if(!count){
        	cur^=B;
        }
        temp=max(1,N-i-1);
        while(temp%2==0){
            temp>>=1;
            ++count;
        }
        temp=i+1;
        while(temp%2==0){
            temp>>=1;
            --count;
        }
    }
    if(flg){
        ans=(ans<<1)%mod;
    }
    cout<<(flg&&!cur?0:ans)<<endl;
}