#include <iostream>
#include <cstdio>
#include <cstring>
#include <algorithm>
using namespace std;

const int maxn=155;
int c[maxn][maxn];
int ans,d[maxn];
int sum;
int n;

inline void pre(){
	for(int i=0;i<=n;i++){
		c[i][0]=1;
		for(int j=1;j<=i;j++)
			c[i][j]=c[i-1][j]+c[i-1][j-1];
	}
}

int main(){
	cin>>n;
	if(n==1){
		cin>>d[1];
		if(d[1]==0) cout<<1<<endl;
		else cout<<0<<endl;
		return 0;
	}
	pre();
	for(int i=1;i<=n;i++){
		cin>>d[i];
		if(!d[i]) return cout<<0<<endl,0;
		d[i]--;
		sum+=d[i];
	}
	if(sum!=n-2) return cout<<0<<endl,0;
	sum=0,ans=1;
	for(int i=1;i<=n;i++)
		ans*=c[n-2-sum][d[i]],sum+=d[i];
	cout<<ans<<endl;
	return 0;
}