#include<bits/stdc++.h>
#define int long long
//#define int __int128
#define ll long long
#define pa pair<int,int>
//#define int unsigned long long
#define sg signed
#define fi first
#define se second
#define ls s[x][0]
#define rs s[x][1]
#define ld long double
#define bs basic_string
const int inf=1e18;
const int mod=998244353;
using namespace std;
inline int read(){
    int s=0,w=1;
    char ch=getchar();
    while(ch<'0'||ch>'9') {
        if(ch=='-')w=-1;
        ch=getchar();
    }
    while(ch<='9'&&ch>='0')
        s=s*10+ch-'0',ch=getchar();
    return s*w;
}
int n,a[1000005],in[2000005],inv[2000005];
int lst[1000005];
int sum[1000005];
int mi(int x,int y){
	int ans=1,base=x;
	while(y){
		if(y&1)ans=(ans*base)%mod;
		base=(base*base)%mod;
		y>>=1;
	}
	return ans;
}
int C(int x,int y){
	if(x<y||x<0||y<0)return 0;
	return in[x]*inv[y]%mod*inv[x-y]%mod;
}
int get(int x,int y){
	return C(x+y,x)-C(x+y,y+2);
}
void solve(){
	n=read();
	for(int i=1;i<=n;i++)a[i]=read();
	in[0]=1;
	for(int i=1;i<=2*n;i++)in[i]=(in[i-1]*i)%mod;
	inv[2*n]=mi(in[2*n],mod-2);
	for(int i=2*n-1;i>=0;i--)inv[i]=(inv[i+1]*(i+1))%mod;
	for(int i=1;i<=n;i++){
		if(a[i-1]==a[i])lst[i]=lst[i-1];
		else lst[i]=i-1;
	}
	sum[0]=1;
	for(int i=1;i<=n;i++){
		if(a[i]==1)break;
		if(a[i]==2)sum[i]=sum[lst[i]];
		else sum[i]=sum[lst[i]]*get(i-lst[i],i-lst[i])%mod;
//		cout<<i<<" "<<sum[i]<<endl;
	}
	int ans=0;
	if(a[n]==1)ans=sum[n-1];
	else for(int i=n;i>=0;i--){
		if(a[i]==3){
			ans=(ans+sum[lst[i]]*get(i-lst[i],n-lst[i]))%mod;
		}else if(a[i]==2)ans=(ans+sum[i])%mod;
		else if(!i)ans=(ans+1)%mod;
		if(a[i]!=2)break;
	}
	cout<<(ans+mod)%mod;
}
signed main(){
	int t=1;while(t--)solve();
    return 0;
}