#include "bits/stdc++.h"

//#include <atcoder/all>

using namespace std;
//using namespace atcoder;

//#define int long long
#define ll long long

ll INF = (1LL << 60);
int mod = 1000000007;
using P = pair<int, int>;

signed main() {
	int N; cin >> N;
	vector<ll>A(N); for (int i = 0; i < N; i++)cin >> A[i];
	for (int i = 0; i < N; i++) {
		if (A[i] == 0) {
			cout << -1 << endl; return 0;
		}
	}
	ll now = 1;
	for (int i = 0; i < N; i++) {
		if (now >= mod) {
			cout << mod << endl; return 0;
		}
		if (A[i] == 1) {
			
		}
		else if (A[i] == 2) {
			now *= 4;
		}
		else if (A[i] == 3) {
			now *= 3 * 3 * 3 * 3 * 3 * 3;
		}
		else {
			cout << mod << endl; return 0;
		}
	}
	if (now >= mod) {
		cout << mod << endl; return 0;
	}
	cout << mod % now << endl;
	return 0;
}