#include<bits/stdc++.h>
using namespace std;
#define int long long
#define vi vector<int>
#define ff first
#define ss second
#define file_se_input  freopen("input.txt", "r", stdin); freopen("output.txt", "w", stdout);
#define pp long long int
#define setbits(x)      __builtin_popcountll(x)
#define zrobits(x)      __builtin_ctzll(x)
#define pb push_back
#define mp make_pair
#define pi 3.141592653589793238
#define eb emplace_back
#define rep(i,a,b) for (int i = a; i <= b; i++)
#define zip(i,a,b) for(int i=a;i<b;i++)
#define rzip(i,a,b) for(int i=a;i>=b;i--)
#define ll unsigned long long int
#define test int t;cin>>t; while(t--)
#define um unordered_map
#define en '\n'
#define us unordered_set
typedef pair<int, int>     pii;
typedef pair<char, int>    pci;
typedef pair<char, char>   pcc;
typedef vector<pii>       vii;
typedef long double ld;
#define all(v) v.begin(), v.end()
#define INF (1e18+5)
#define inf (1e9+5)
#define mod 1000000007


bool check_prime(long long n)
{
	int flag = 0;
	for (long long i = 2; i * i <= n; i++)
	{
		if (n % i == 0)
		{
			flag = 1;
			break;
		}
	}
	if (n == 1)
		return false;
	else if (flag == 0 || n == 2 || n == 3)
	{
		return true;
	}
	else
	{
		return false;
	}

}

int BE(int x, int n, int m) //function to calculate x raise to power n modulo m
{
	int result = 1;
	while (n > 0)
	{
		if (n % 2 == 1)
			result = result * x % m;
		x = x * x % m;
		n = n / 2;
	}
	return result;
}

int c[3];
int32_t main()
{
	ios_base::sync_with_stdio(false);
	cin.tie(NULL);
	cout.tie(0);
#ifndef ONLINE_JUDGE
	if (fopen("input.txt", "r"))
	{
		freopen ("input.txt" , "r" , stdin);
		freopen ("output.txt" , "w" , stdout);
	}
#endif
	//_______________________________-code starts-_______________________________________________

	int n;
	cin >> n;
	int a[n];
	zip(i, 0, n)
	{
		cin >> a[i];
	}
	int ans = 1;
	zip(i, 0, n)
	{
		int cnt = 0;
		int id = -1;
		if (a[i] == c[0]) cnt++, id = 0;
		if (a[i] == c[1]) cnt++, id = 1;
		if (a[i] == c[2]) cnt++, id = 2;
		if (id == -1)
		{
			cout << 0 << en;
			return 0;
		}
		ans = (ans * cnt) % mod;
		c[id]++;
	}
	cout << ans << en;

	return 0;
}


#include <bits/stdc++.h>
using namespace std;

#define rep(i, a) for (int i = 0; i < (a); i++ )
#define FOR(i, m, n) for(int i = m; i < n; i++)
 
typedef pair<int,int> P;
typedef long long ll;
 
const int INF = 1001001001;
const int MOD = 1000000007;
const double PI=acos(-1);

int main(){
    ll N;
    cin >> N;

    ll c[3] = {};
    ll ans = 1;

    rep(i,N) {
        ll a;
        cin >> a;
        bool t = false;
        ll cnt = 0;
        rep(j,3) {
            if (c[j]==a && !t) {
                c[j]++;
                cnt++;
                t = true;
            }
            else if (c[j]==a) {
                cnt++;
            }
        }
        ans*=cnt;
        ans%=MOD;
    }
    cout << ans << endl;
}
