#include <bits/stdc++.h>
#define REP(i, n) for (int i = 0; (i) < (int)(n); ++ (i))
#define REP3(i, m, n) for (int i = (m); (i) < (int)(n); ++ (i))
#define REP_R(i, n) for (int i = (int)(n) - 1; (i) >= 0; -- (i))
#define REP3R(i, m, n) for (int i = (int)(n) - 1; (i) >= (int)(m); -- (i))
#define ALL(x) std::begin(x), std::end(x)
#define dump(x) cerr << #x " = " << x << endl
using namespace std;
template <class T> using reversed_priority_queue = priority_queue<T, vector<T>, greater<T> >;
template <class T, class U> inline void chmax(T & a, U const & b) { a = max<T>(a, b); }
template <class T, class U> inline void chmin(T & a, U const & b) { a = min<T>(a, b); }
template <typename X, typename T> auto make_table(X x, T a) { return vector<T>(x, a); }
template <typename X, typename Y, typename Z, typename... Zs> auto make_table(X x, Y y, Z z, Zs... zs) { auto cont = make_table(y, z, zs...); return vector<decltype(cont)>(x, cont); }
template <typename T> ostream & operator << (ostream & out, vector<T> const & xs) { REP (i, (int)xs.size() - 1) out << xs[i] << ' '; if (not xs.empty()) out << xs.back(); return out; }
template<typename Functor> struct fix_type { Functor functor; template<typename... Args> decltype(auto) operator() (Args && ... args) const & { return functor(functor, std::forward<Args>(args)...); } };
template<typename Functor> fix_type<typename std::decay<Functor>::type> fix(Functor && functor) { return { std::forward<Functor>(functor) }; }

template <int32_t MOD>
struct mint {
    int32_t value;
    mint() : value() {}
    mint(int64_t value_) : value(value_ < 0 ? value_ % MOD + MOD : value_ >= MOD ? value_ % MOD : value_) {}
    mint(int32_t value_, std::nullptr_t) : value(value_) {}
    explicit operator bool() const { return value; }
    inline constexpr mint<MOD> operator + (mint<MOD> other) const { return mint<MOD>(*this) += other; }
    inline constexpr mint<MOD> operator - (mint<MOD> other) const { return mint<MOD>(*this) -= other; }
    inline constexpr mint<MOD> operator * (mint<MOD> other) const { return mint<MOD>(*this) *= other; }
    inline constexpr mint<MOD> & operator += (mint<MOD> other) { this->value += other.value; if (this->value >= MOD) this->value -= MOD; return *this; }
    inline constexpr mint<MOD> & operator -= (mint<MOD> other) { this->value -= other.value; if (this->value <    0) this->value += MOD; return *this; }
    inline constexpr mint<MOD> & operator *= (mint<MOD> other) { this->value = (uint_fast64_t)this->value * other.value % MOD; return *this; }
};
template <int32_t MOD> std::istream & operator >> (std::istream & in, mint<MOD> & n) { int64_t value; in >> value; n = value; return in; }
template <int32_t MOD> std::ostream & operator << (std::ostream & out, mint<MOD> n) { return out << n.value; }

constexpr int MOD = 1e9 + 7;
mint<MOD> solve(int n, const vector<int> & a) {
    map<tuple<int, int, int>, mint<MOD> > cur;
    cur[make_tuple(0, 0, 0)] += 1;
    for (int a_i : a) {
        map<tuple<int, int, int>, mint<MOD> > prv;
        cur.swap(prv);
        for (auto it : prv) {
            int x, y, z; tie(x, y, z) = it.first;
            mint<MOD> cnt = it.second;
            if (x == a_i) cur[make_tuple(x + 1, y, z)] += cnt;
            if (y == a_i) cur[make_tuple(x, y + 1, z)] += cnt;
            if (z == a_i) cur[make_tuple(x, y, z + 1)] += cnt;
        }
    }
    mint<MOD> answer = 0;
    for (auto it : cur) {
        answer += it.second;
    }
    return answer;
}

int main() {
    int n; cin >> n;
    vector<int> a(n);
    REP (i, n) {
        cin >> a[i];
    }
    cout << solve(n, a) << endl;
    return 0;
}


Measured memory_bytes: 640