#include <iostream>
#include <string>
#include <algorithm>
#include <cstdlib>
#include <cmath>
#include <vector>
#include <list>
#include <cstdint>
#include <bits/stdc++.h>
#include <queue>
#include <set>

#define rep(i, n) for (int i = 0; i < (int)(n); i++)
#define rep_r(i, n) for (int i = n - 1; i >= 0; i--)
#define rep1(i, n) for (int i = 1; i <= (int)(n); i++)
#define REP(i, n) for (int i = 0, i##_len = (n); i < i##_len; ++i)
#define all(x) (x).begin(), (x).end()
#define SZ(x) ((ll)(x).size())
#define bit(n) (1LL << (n))
#define UNIQUE(v) v.erase(unique(v.begin(), v.end()), v.end());

#define INF bit(60)
#define pb push_back
#define mod 1000000007

template <class T>
bool chmax(T &a, const T &b)
{
  if (a < b)
  {
    a = b;
    return 1;
  }
  return 0;
}
template <class T>
bool chmin(T &a, const T &b)
{
  if (b < a)
  {
    a = b;
    return 1;
  }
  return 0;
}

using namespace std;
using uif = uint_fast64_t;
using ll = long long int;

int qp(int a, ll b)
{
  int ans = 1;
  do
  {
    if (b & 1)
      ans = 1ll * ans * a % mod;
    a = 1ll * a * a % mod;
  } while (b >>= 1);
  return ans;
}
int qp(int a, ll b, int mo)
{
  int ans = 1;
  do
  {
    if (b & 1)
      ans = 1ll * ans * a % mo;
    a = 1ll * a * a % mo;
  } while (b >>= 1);
  return ans;
}

int gcd(int a, int b) { return b ? gcd(b, a % b) : a; }
int dx[4] = {1, 0, -1, 0};
int dy[4] = {0, 1, 0, -1};

#define FACSIZE 2002

ll invfac[FACSIZE];
ll fac[FACSIZE];

ll mod_pow(ll, ll);
ll mod_add(ll, ll);
ll mod_mul(ll, ll);
ll mod_div(ll, ll);
void make_fact(ll);
void make_invfact(ll);

int main(void)
{

  ll n;
  cin >> n;
  vector<ll> a(n);
  rep(i, n) cin >> a[i];

  if (n == 1)
  {
    cout << 3 << endl;
    return 0;
  }

  map<ll, ll> m;

  if (a[0] != 0)
  {
    cout << 0 << endl;
    return 0;
  }

  ll ans = 3;
  m[0] = 1;

  vector<ll> dp(n, 0);

  for (ll i = 1; i < n; i++)
  {
    ll x = a[i];
    if (m.lower_bound(x - 1) == end(m))
    {
      cout << 0 << endl;
      return 0;
    }

    if (x == 0)
    {
      if (m[0] == 1)
      {
        ans = 6;
      }
      else if (m[0] == 2)
      {
      }
      else if (m[0] >= 3)
      {
        cout << 0 << endl;
        return 0;
      }
    }
    else if (m.find(x) != end(m))
    {
      if (m[x] >= m[x - 1] || m[x] >= 3)
      {
        cout << 0 << endl;
        return 0;
      }
      ans = (ans % mod) * ((m[x - 1] - m[x]) % mod);
    }
    else
    {

      ans = (ans % mod) * (m[x - 1] % mod);
    }

    if (m.find(x) != end(m))
      m[x]++;
    else
      m[x] = 1;
  }

  cout << ans % mod << endl;

  return 0;
}

ll mod_pow(ll x, ll r)
{
  if (r == 0)
    return 1;
  else if (r == 1)
    return x % mod;
  else if (r % 2 == 0)
  {
    ll t = mod_pow(x, r / 2) % mod;
    return t * t % mod;
  }
  else
  {
    ll t = mod_pow(x, r / 2) % mod;
    ll k = t * t % mod;
    return k * x % mod;
  }
}
ll mod_add(ll a, ll b)
{
  return (a + b) % mod;
}

ll mod_mul(ll a, ll b)
{
  return (a * b) % mod;
}

ll mod_div(ll a, ll b)
{
  return mod_mul(a, mod_pow(b, mod - 2));
}

void make_fact(ll n)
{
  fac[0] = 1;
  rep(i, n)
  {
    fac[i + 1] = mod_mul(fac[i], i + 1);
  }
}

void make_invfact(ll n)
{
  invfac[n] = mod_pow(fac[n], mod - 2);
  for (int i = n - 1; i >= 0; i--)
  {
    invfac[i] = mod_mul(invfac[i + 1], i + 1);
  }
}

Measured memory_bytes: 8064