// what is matter? never mind. 
#pragma GCC optimize("Ofast")
#pragma GCC optimize("unroll-loops")
//#pragma GCC target("sse,sse2,sse3,sse4,popcnt,abm,mmx,avx,avx2")
#include<bits/stdc++.h>
#define For(i,a,b) for(int i=(a);i<=(b);++i)
#define Rep(i,a,b) for(int i=(a);i>=(b);--i)
#define ll long long
#define ull unsigned long long
//#define int long long
#define SZ(x) ((int)((x).size()))
#define ALL(x) (x).begin(),(x).end()
using namespace std;
inline int read()
{
	char c=getchar();int x=0;bool f=0;
	for(;!isdigit(c);c=getchar())f^=!(c^45);
	for(;isdigit(c);c=getchar())x=(x<<1)+(x<<3)+(c^48);
	return f?-x:x;
}

#define mod 998244353
struct modint{
	unsigned int x;
	modint(int o=0){x=o;}
	modint &operator = (int o){return x=o,*this;}
	modint &operator +=(modint o){return x=x+o.x>=mod?x+o.x-mod:x+o.x,*this;}
	modint &operator -=(modint o){return x=x<o.x?x-o.x+mod:x-o.x,*this;}
	modint &operator *=(modint o){return x=1ll*x*o.x%mod,*this;}
	modint &operator ^=(int b){
		modint a=*this,c=1;
		for(;b;b>>=1,a*=a)if(b&1)c*=a;
		return x=c.x,*this;
	}
	modint &operator /=(modint o){return *this *=o^=mod-2;}
	friend modint operator +(modint a,modint b){return a+=b;}
	friend modint operator -(modint a,modint b){return a-=b;}
	friend modint operator *(modint a,modint b){return a*=b;}
	friend modint operator /(modint a,modint b){return a/=b;}
	friend modint operator ^(modint a,int b){return a^=b;}
	friend bool operator ==(modint a,modint b){return a.x==b.x;}
	friend bool operator !=(modint a,modint b){return a.x!=b.x;}
	bool operator ! () {return !x;}
	modint operator - () {return x?mod-x:0;}
	bool operator <(const modint&b)const{return x<b.x;}
};
inline modint qpow(modint x,int y){return x^y;}

vector<modint> fac,ifac,iv;
inline void initC(int n)
{
	if(iv.empty())fac=ifac=iv=vector<modint>(2,1);
	int m=iv.size(); ++n;
	if(m>=n)return;
	iv.resize(n),fac.resize(n),ifac.resize(n);
	For(i,m,n-1){
		iv[i]=iv[mod%i]*(mod-mod/i);
		fac[i]=fac[i-1]*i,ifac[i]=ifac[i-1]*iv[i];
	}
}
inline modint C(int n,int m){
	if(m<0||n<m)return 0;
	return initC(n),fac[n]*ifac[m]*ifac[n-m];
}
inline modint sign(int n){return (n&1)?(mod-1):(1);}

#define fi first
#define se second
#define pb push_back
#define mkp make_pair
typedef pair<int,ll>pii;
typedef vector<int>vi;

#define maxn 2000005
#define inf 0x3f3f3f3f

int n,a[maxn];

modint F(int len){
	modint res=C(len*2,len);
	res-=C(len*2,len+2);
	return res;
}
modint G(int len,int cnt){
	int up=len+cnt,dw=len;
	modint res=C(up+dw,up);
	res-=C(up+dw,up+2);
	return res;
}

signed main()
{
//	For(i,1,10) cout<<F(i).x<<" "; cout<<"\n";
	n=read();
	For(i,1,n)a[i]=read();
	For(i,1,n-1)if(a[i]==1)puts("0"),exit(0);
	int pos=n,cnt=0,hav=0;
	if(a[pos]==1) hav=1,--pos;
	while(pos>0 && a[pos]==2) ++cnt,--pos;
	if(pos==0){
		if(hav)puts("1");
		else cout<<cnt+1<<"\n";
		exit(0);
	}
	bool fir=1;
	modint res=1;
	
	while(pos>0){
		int p2=pos,len=0;
		while(p2>0 && a[p2]==3) --p2,++len;
		
	//	len=999999;
//		if(n==1000000)cout<<"len "<<len<<" "<<a[n]<<"\n";
		
		if(hav){
			res*=F(len);
		}else{
			modint tmp=0;
			if(fir){
		///		cout<<"G "<<G(len,cnt).x<<"\n";
		//		cout<<"F "<<F(len).x<<"\n";
				tmp+=G(len,cnt);
				tmp+=cnt*F(len);
			}else{
				tmp+=F(len);
			}
			res*=tmp;
		}
		
		while(p2>0 && a[p2]==2) --p2;
		pos=p2; fir=0;
	}
	cout<<res.x;
	return 0;
}
/*
3
3 3 2
2 2 2 1 1

1 1 2 2 2
2 2 2

? ? 1 1x`


(12=3)  1 1 1 1 1 
*/