#include<iostream>
using namespace std;

const int MOD = 1e9 + 7;
long long n, c0 = 0, c1 = 0;
bool f[1005];
long long C[1005], ans = 0;

long long qpow(long long k){
	long long res = 1, a = 2;
	while(k){
		if(k & 1) res = res * a % MOD;
		a = a * a % MOD;
		k >>= 1;
	}
	return res;
}

int main(){
	freopen("01.in", "r", stdin);
	freopen("01.out", "w", stdout);
	cin.tie(0); ios::sync_with_stdio(0);
	cin >> n;
	for(int i = 1;i <= n;i ++){
		cin >> f[i];
		if(f[i]) c1 ++;
		else c0 ++;
	}
	C[0] = 1;
	for(int i = 1;i <= n;i ++){
		for(int j = i;j >= 1;j --){
			C[j] = (C[j] + C[j - 1]) % MOD;
		}
	}
	for(int m = 0;m <= n;m ++){
		long long cnt = 1ll * c0 * (n - m) + 1ll * c1 * m;
		ans = (ans + C[m] * qpow(cnt)) % MOD;
	}
	cout << ans << '\n';
	return 0;
}