//
//  main.cpp
//

#include <algorithm>
#include <array>
#include <assert.h>
#include <iomanip>
#include <iostream>
#include <limits>
#include <math.h>
#include <memory>
#include <memory>
#include <queue>
#include <random>
#include <set>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <string>
#include <tuple>
#include <unordered_map>
#include <unordered_set>
#include <vector>

using namespace std;

using ll = int64_t;
using ull = uint64_t;

template<typename T>
vector<T> make_vec_nd(T init, ll size) {
    return vector<T>(size, init);
}
template<typename T, typename... Args>
auto make_vec_nd(T init, ll size, Args... rest) {
    auto inner = make_vec_nd(init, rest...);
    return vector<decltype(inner)>(size, inner);
}

#define rep(i,a,b) for(ll i=(a);i<(b);i++)
#define rrep(i,a,b) for(ll i=(a)-1;i>=(b);i--)

struct Mod {
    static ll BASE;
    ll value = 0;
    static ll residue(ll value) { return (value % BASE + BASE) % BASE; }
    Mod()
    : value(0) {}
    Mod(ll value)
    : value(residue(value)) {}
    Mod operator+(const Mod& rhs) const { return Mod(value + rhs.value); }
    void operator+=(const Mod& rhs) { *this = *this + rhs; }
    Mod operator-(const Mod& rhs) const { return Mod(value - rhs.value); }
    void operator-=(const Mod& rhs) { *this = *this - rhs; }
    Mod operator*(const Mod& rhs) const { return Mod(value * rhs.value); }
    void operator*=(const Mod& rhs) { *this = *this * rhs; }
    Mod operator/(const Mod& rhs) const { return *this * rhs.inv(); }
    void operator/=(const Mod& rhs) { *this = *this / rhs; }
    Mod inv() const {
        if (value == 0) {
            assert(false);
            throw "[Mod::inv] div by zero";
        }
        ll ans, sub;
        ll d = Mod::gcd_with_coef(value, BASE, ans, sub);
        if (d != 1) {
            assert(false);
            throw "[Mod::inv] not invertible";
        }
        return ans;
    }
    static ll gcd_with_coef(ll x, ll y, ll& out_cx, ll& out_cy) {
        if (x < 0) {
            ll d = gcd_with_coef(-x, y, out_cx, out_cy);
            out_cx *= -1;
            return d;
        }
        if (y < 0) {
            ll d = gcd_with_coef(x, -y, out_cx, out_cy);
            out_cy *= -1;
            return d;
        }
        if (x > y) {
            return gcd_with_coef(y, x, out_cy, out_cx);
        }
        if (x == 0) {
            out_cx = 0;
            out_cy = 1;
            return y;
        }
        ll q = y / x;
        ll r = y % x;
        ll d = gcd_with_coef(r, x, out_cy, out_cx);
        out_cx -= q * out_cy;
        return d;
    }
    static vector<vector<Mod>> binom_table(ll n) {
        vector<vector<Mod>> ans;
        auto get = [&ans](ll r, ll k) -> Mod {
            if (r < 0 || k < 0 || k > r) {
                return Mod(0);
            } else {
                return ans[r][k];
            }
        };
        ans.push_back({Mod(1)});
        for (ll r = 1; r <= n; r++) {
            ans.push_back(vector<Mod>());
            for (ll k = 0; k <= r; k++) {
                ans[r].push_back(get(r - 1, k) + get(r - 1, k - 1));
            }
        }
        return ans;
    }
    static Mod power(Mod base, ll n) {
        assert(n >= 0);
        Mod ans(1);
        Mod pow(base);
        for (int i = 0; i < 63; i++) {
            if ((n >> i) & 1) {
                ans *= pow;
            }
            pow = pow * pow;
        }
        return ans;
    }
};
ll Mod::BASE = 1000000007;

int main() {
    ll N;
    cin >> N;
    vector<ll> Ais(N);
    rep(i,0,N) {
        cin >> Ais[i];
    }
    vector<ll> count(3);
    Mod ans = 1;
    rep(i,0,N) {
        ll Ai = Ais[i];
        ll matches = 0;
        ll first_match = numeric_limits<ll>::max();
        rep(col,0,3) {
            if (count[col] == Ai) {
                matches++;
                first_match = min(first_match, col);
            }
        }
        if (matches == 0) {
            cout << 0 << endl;
            return 0;
        }
        ans *= matches;
        count[first_match]++;
    }
    cout << ans.value << endl;
}



Measured memory_bytes: 1024