#include <bits/stdc++.h>
using namespace std;
 
#define fi first
#define se second
#define pb push_back
using vi = vector <int>;
using ll = long long;
using vl = vector <ll>;
using pii = pair <int, int>;
//~ const ll mod = 998244353;
const ll mod = 1e9 + 7;
ll qpow(ll a, ll b, ll m = mod) { ll r = 1, t = a;
	for(; b; b /= 2) { if(b & 1) r = r * t % m; t = t * t % m; } return r; }


int main() {
	ios :: sync_with_stdio(false);
	
	int n; cin >> n;
	
	ll mul = 1;
	ll c[4] = {0, 1, 4, 729};
	for(int i = 1; i <= n; i ++) {
		ll a; cin >> a;
		if(a >= 4) mul = 1e9 + 8;
		else if(a == 0) {
			cout << "-1\n";
			return 0;
		} else {
			mul = mul * c[a];
			if(mul >= 1e9 + 8)
				mul = 1e9 + 8;
		}
	}
	
	cout << (ll)(1e9 + 7) % mul << '\n';
}