#line 1 "a.cpp"
#include<iostream>
using namespace std;
#line 3 "/home/kotatsugame/library/math/modint.cpp"
#include<utility>
template<int m>
struct modint{
	unsigned int x;
	constexpr modint()noexcept:x(){}
	template<typename T>
	constexpr modint(T x_)noexcept:x((x_%=m)<0?x_+m:x_){}
	constexpr unsigned int val()const noexcept{return x;}
	constexpr modint&operator++()noexcept{if(++x==m)x=0;return*this;}
	constexpr modint&operator--()noexcept{if(x==0)x=m;--x;return*this;}
	constexpr modint operator++(int)noexcept{modint res=*this;++*this;return res;}
	constexpr modint operator--(int)noexcept{modint res=*this;--*this;return res;}
	constexpr modint&operator+=(const modint&a)noexcept{x+=a.x;if(x>=m)x-=m;return*this;}
	constexpr modint&operator-=(const modint&a)noexcept{if(x<a.x)x+=m;x-=a.x;return*this;}
	constexpr modint&operator*=(const modint&a)noexcept{x=(unsigned long long)x*a.x%m;return*this;}
	constexpr modint&operator/=(const modint&a)noexcept{return*this*=a.inv();}
	constexpr modint operator+()const noexcept{return*this;}
	constexpr modint operator-()const noexcept{return modint()-*this;}
	constexpr modint pow(long long n)const noexcept
	{
		if(n<0)return pow(-n).inv();
		modint x=*this,r=1;
		for(;n;x*=x,n>>=1)if(n&1)r*=x;
		return r;
	}
	constexpr modint inv()const noexcept
	{
		int s=x,t=m,x=1,u=0;
		while(t)
		{
			int k=s/t;
			s-=k*t;
			swap(s,t);
			x-=k*u;
			swap(x,u);
		}
		return modint(x);
	}
	friend constexpr modint operator+(const modint&a,const modint&b){return modint(a)+=b;}
	friend constexpr modint operator-(const modint&a,const modint&b){return modint(a)-=b;}
	friend constexpr modint operator*(const modint&a,const modint&b){return modint(a)*=b;}
	friend constexpr modint operator/(const modint&a,const modint&b){return modint(a)/=b;}
	friend constexpr bool operator==(const modint&a,const modint&b){return a.x==b.x;}
	friend constexpr bool operator!=(const modint&a,const modint&b){return a.x!=b.x;}
	friend ostream&operator<<(ostream&os,const modint&a){return os<<a.x;}
	friend istream&operator>>(istream&is,modint&a){long long v;is>>v;a=modint(v);return is;}
};
#line 4 "a.cpp"
using mint=modint<998244353>;
int N,A[2<<17];
mint p[2<<17];
main()
{
	cin>>N;
	p[0]=1;
	for(int i=0;i<N;i++)
	{
		cin>>A[i];
		p[i+1]=p[i]*2;
	}
	mint ans=0;
	for(int i=0;i<N;i++)if(A[i]==2||A[i]==-2)
	{
		mint L[2],R[2];
		L[0]=p[i>0?i-1:0];
		R[0]=p[N-i-1>0?N-i-2:0];
		int f=0;
		for(int j=i-1;j>=0;j--)
		{
			if(A[j]!=1&&A[j]!=-1)break;
			if(A[j]==-1)f=1-f;
			L[f]+=p[j>0?j-1:0];
		}
		f=0;
		for(int j=i+1;j<N;j++)
		{
			if(A[j]!=1&&A[j]!=-1)break;
			if(A[j]==-1)f=1-f;
			R[f]+=p[N-j-1>0?N-j-2:0];
		}
		if(A[i]==2)ans+=L[0]*R[1]+L[1]*R[0];
		else ans+=L[0]*R[0]+L[1]*R[1];
	}
	ans/=p[N-1];
	cout<<ans<<endl;
}