/* Author haleyk10198 */
/* 作者:  haleyk10198 */
/* CF handle: haleyk100198*/
#include <bits/stdc++.h>

#define MOD 1000000007
#define LINF (1LL<<60)
#define INF 2147483647
#define PI 3.1415926535897932384626433
#define ll long long
#define pii pair<int,int>
#define mp(x,y) make_pair((x),(y))
#define pb(x) push_back((x))

using namespace std;

string itos(int x){
	stringstream ss;
	ss << x;
	return ss.str();
}

int res, n, d[55], dp[55][55], sum[55];

int pwr(int b, int e){
	if(e == 0) return 1;
	if(e == 1) return b;
	return (1LL*pwr((1LL*b*b)%MOD, e/2)*pwr(b, e%2))%MOD;
}

void upd(int &tar, int val){
	(tar += val) %= MOD;
}

int help(int l, int r, int deb1, int deb2){
	if(deb1 < 0 || deb2 < 0) return 0;
	if(l > r)
		return deb1 == 0 && deb2 == 0;
	int res = 0, deb = deb1+deb2;
	vector<int> v1(4), v2(4);
	v1[0] = 1, v1[1] = deb1, v1[2] = (deb1-1)*deb1/2, v1[3] = (deb1-2)*(deb1-1)*deb1/6;
	v2[0] = 1, v2[1] = deb1, v2[2] = (deb2-1)*deb2/2, v2[3] = (deb2-2)*(deb2-1)*deb2/6;
	for(int ret = d[l]; ret >= 0; ret--){
		if(ret == d[l])
			for(int j = 0; j <= ret; j++)
				upd(res, (1LL*v1[j]*v2[ret-j]*help(l+1, r, deb1-j+(ret-j), deb2-(ret-j)))%MOD);
		else if(ret == 0)
			upd(res, help(l+1, r, deb1+(d[l] == 1), deb2+(d[l] == 2)));
		else
			upd(res, (1LL*deb1*help(l+1, r, deb1, deb2)+1LL*deb2*help(l+1, r, deb1+2, deb2-1))%MOD);			
	}
	return res;
}

int dpf(int l, int r){
	if(r == n-1) return 1;
	if(r >= n) return 0;
	if(dp[l][r] != -1) return dp[l][r];
	dp[l][r] = 0;
	for(int i = 1; i <= min(n-1-r, sum[r+1]-sum[l]); i++){
		int val = help(l, r, i, 0);
		if(val)
			(dp[l][r] += (1LL*val*dpf(r+1, r+i))%MOD) %= MOD;
	}
	return dp[l][r];
}

int main(){
	//freopen("input.txt","r",stdin);
	//freopen("output.txt","w",stdout);
	ios_base::sync_with_stdio(false);
	cin >> n;
	for(int i = 0; i < 55; i++) for(int j = 0; j < 55; j++) dp[i][j]--;
	for(int i = 0; i < n; i++)
		cin >> d[i];
	for(int i = 1; i < n; i++) d[i]--;
	for(int i = 1; i <= n; i++)	sum[i] = sum[i-1]+d[i-1];
	cout << dpf(0, 0) << endl;
	return 0;
}