#include<bits/stdc++.h>
#define ll long long
using namespace std;

inline ll read(){
	ll s=0,k=1;
	char c=getchar();
	while(c>'9'||c<'0'){
		if(c=='-') k=-1;
		c=getchar();
	}
	while(c>='0'&&c<='9'){
		s=(s<<3)+(s<<1)+(c^48);
		c=getchar();
	}
	return s*k;
}

const int N=1e6+10,mod=998244353;
ll n,a[N],fac[N<<1],inv[N<<1];

ll ksm(ll a,ll b){
	ll t=1;
	for(;b;b>>=1,a=a*a%mod)
		if(b&1) t=t*a%mod;
	return t;
}

ll C(ll n,ll m){
	if(n<m) return 0;
	return fac[n]*inv[m]%mod*inv[n-m]%mod;
}

ll Cat(ll n,ll m){
	if(m<2) return C(n+m,m);
	else if(m-n<2) return (C(n+m,m)-C(n+m,m-2)+mod)%mod;
	else return 0;
}

int main(){
//	freopen(".in","r",stdin);
//	freopen(".out","w",stdout);
	n=read();
	fac[0]=1;
	for(int i=1;i<=n<<1;i++) fac[i]=fac[i-1]*i%mod;
	inv[n<<1]=ksm(fac[n<<1],mod-2);
	for(int i=n*2-1;i>=0;i--) inv[i]=inv[i+1]*(i+1)%mod;
	for(int i=1;i<=n;i++) a[i]=read();
	for(int i=1;i<n;i++)
		if(a[i]==1) return puts("0"),0;
	vector<ll>vec;
	for(int i=1,j;i<=n;i++){
		if(a[i]!=3) continue;
		j=i;
		while(j<=n&&a[j]==3) j++;
		vec.push_back(j-i);
		i=j;
	}
	ll ans=1;
	if(a[n]==2){
		ll len=1;
		for(int i=n-1;i>=1;i--) 
			if(a[i]==2) len++;
			else break;
		if(vec.size()==0){
			printf("%lld",len+1);
			return 0;
		}
		(ans*=(Cat(vec.back(),vec.back())*len%mod+Cat(vec.back()+len,vec.back()))%mod)%=mod;
		vec.pop_back();
		for(auto x:vec) (ans*=Cat(x,x))%=mod;
	}
	else for(auto x:vec) (ans*=Cat(x,x))%=mod;
	printf("%lld",ans);
	return 0;
}