codeforces #309 A

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

typedef long long LL;
const int mod=1000000007;
const int maxn=1010;
int n,m;
int Num[maxn],sum[maxn];
int f[maxn][maxn];
int C[maxn][maxn];
int S[maxn][maxn];
//f(i,j)????????i?????j???????????????? 

void pre_C(){
	C[0][0]=1;
	for(int i=1;i<=1000;++i){
		C[i][0]=C[i][i]=1;
		for(int j=1;j<i;++j){
			C[i][j]=C[i-1][j-1]+C[i-1][j];
			if(C[i][j]>=mod)C[i][j]-=mod;
		}
	}return;
}

int main(){
	scanf("%d",&n);
	for(int i=1;i<=n;++i)scanf("%d",&Num[i]),m+=Num[i],sum[i]=sum[i-1]+Num[i];
	pre_C();
	f[0][0]=1;S[0][0]=1;
	for(int i=1;i<=m;++i)S[i][0]=1;
	for(int j=1;j<=n;++j){
		for(int i=1;i<=m;++i){
			if(i>=sum[j])f[i][j]=1LL*S[i-1][j-1]*C[i-1-sum[j-1]][Num[j]-1]%mod;
			else f[i][j]=0;
			S[i][j]=f[i][j]+S[i-1][j];
			if(S[i][j]>=mod)S[i][j]-=mod;
		}
	}cout<<f[m][n]<<endl;
	return 0;
	
}