#include <bits/stdc++.h>

const long long m = 1000000007;

using namespace std;

void solve() {
	long long n;
	cin >> n;
	vector<long long> v(n);
	for(int i = 0; i < n; i++) cin >> v[i];
	
	long long threes = 0;
	for(int i = 0; i < n; i++) {
		if(v[i] == 3) threes++;
	}
	
	long long result = 0, a = 0, b = 0, ones = 0;
	for(int i = 0; i < n; i++) {
		if(v[i] == 1) ones++;
		else if (v[i] == 2) {
			long long c = ((a + b) % m + ones) % m;
			result += (c * threes) % m;
			a = b;
			b = c;
		} else if(v[i] == 3) {
			threes--;
		}
	}
	
	cout << result;
}
 
int main(){
	solve();
    return 0;
}