#include<iostream>
using namespace std;
int a[100005];
bool b;
int main(){
	freopen("pingfang.in","r",stdin);
	freopen("pingfang.out","w",stdout);
	int n;
	cin>>n;
	for(int i=1;i<=n;i++){
		cin>>a[i];
		if(a[i]>2){
			b=1;
		}
	}
	if(n==2){
		if(max(a[1],a[2])%min(a[1],a[2])==0){
			cout<<(max(a[1],a[2])/min(a[1],a[2]))%1000000007;
		}else{
			cout<<max(a[1],a[2])*min(a[1],a[2])%1000000007;
		}
	}
	long long ans=1;
	if(b==0){
		for(int i=1;i<=n;i++){
			if(a[i]==2){
				if(a[i+1]==1){
					ans=(ans*2)%1000000007;
				}
				i++;
			}
		}
		cout<<ans;
	}
	fclose(stdin);
	fclose(stdout);
	return 0;
}