#include <stdio.h>
#define rep(E, F) for (E = 0; E < (F); E++)
int get_int();
typedef long long ll;

int main()
{
	ll i, n = get_int(), a = 0, b = 0, c = 0, r = 0, t = 0, m = 1000000007;
	ll x[n];
	rep(i, n) x[i] = get_int();
	rep(i, n) c += x[i] == 3 ? 1 : 0;
	rep(i, n) switch (x[i])
	{
		case 1: a++; break;
		case 2:
				b = (t + a)%m;
				t = (t + b)%m;
				r = (r + (b*c)%m)%m;
				break;
		case 3: c--; break;
	}
	printf("%lld\n", r);
	return 0;
}

int get_int()
{
	int ret = 0;
	char c = getchar();
	int sgn;

	while (1)
	{
		if (c == EOF) return EOF;
		if (c >= '0' && c <= '9') { sgn = 1; break; }
		if (c == '-')
		{
			c = getchar();
			if (c < '0' || c > '9') continue;
			sgn = -1;
			break;
		}
		c = getchar();
	}

	while (1)
	{
		ret = ret*10 + c - '0';
		c = getchar();
		if (c < '0' || c > '9') return sgn*ret;
	}
}