#include <bits/stdc++.h>

using namespace std;

#define DUMP(x) std::cerr << (#x) << " = " << (x) << "\n"
#define rep(i, n) for (int i = 0; i < (int)(n); ++i)
#define REP(i, k, n) for (int i = (k); i < (int)(n); ++i)
#define ALL(r) r.begin(), r.end()
#define YES puts("YES")
#define Yes puts("Yes")
#define NO puts("NO")
#define No puts("No")
#define IMP puts("IMPOSSIBLE")
#define Imp puts("Impossible")
#define imp puts("impossible")
#define M1 puts("-1")
#define pb push_back

template <typename T>
T dup(T x, T y)
{
    return (x + y - 1) / y;
};
template <typename A, size_t N, typename T>
inline void arrayFill(A (&array)[N], const T &val) { std::fill((T *)array, (T *)(array + N), val); }

using ll = int64_t;
using vint = vector<int32_t>;
using vvint = vector<vint>;
using vll = vector<ll>;
using vvll = vector<vll>;
using vstr = vector<string>;
using pint = pair<int32_t, int32_t>;
using pll = pair<ll, ll>;
using setint = set<int32_t>;
using setstr = set<string>;
using qint = queue<int32_t>;
using qpint = queue<pint>;

constexpr std::int32_t INF = 1001001001;
constexpr std::int64_t LINF = 1001001001001001001;

//                  9876543210
constexpr int mod = 998244353;
class mint
{
private:
    std::int64_t m_x;

public:
    mint(std::int64_t m_x = 0) : m_x(m_x % mod) {}
    std::int64_t get() { return m_x; }
    mint &operator+=(const mint a)
    {
        if ((m_x += a.m_x) >= mod)
            m_x -= mod;
        return *this;
    }
    mint &operator-=(const mint a)
    {
        if ((m_x += mod - a.m_x) >= mod)
            m_x -= mod;
        return *this;
    }
    mint &operator*=(const mint a)
    {
        (m_x *= a.m_x) %= mod;
        return *this;
    }
    mint operator+(const mint a) const
    {
        mint res(*this);
        return res += a;
    }
    mint operator-(const mint a) const
    {
        mint res(*this);
        return res -= a;
    }
    mint operator*(const mint a) const
    {
        mint res(*this);
        return res *= a;
    }

    mint pow(const std::int64_t t) const
    {
        if (!t)
            return 1;
        mint a = pow(t >> 1);
        a *= a;
        if (t & 1)
            a *= *this;
        return a;
    }
    // for prime mod
    mint inv() const
    {
        return pow(mod - 2);
    }
    mint &operator/=(const mint a)
    {
        return (*this) *= a.inv();
    }
    mint operator/(const mint a) const
    {
        mint res(*this);
        return res /= a;
    }
};

void Main()
{
    int n;
    cin >> n;
    vint d(n);
    rep(i, n)
    {
        cin >> d[i];
    }

    vint num(n, 0);
    int max_index = 0;
    rep(i, n)
    {
        ++num[d[i]];
        max_index = max(max_index, d[i]);
    }

    if (d[0] != 0 || num[0] != 1)
    {
        cout << 0 << endl;
        return;
    }

    mint ans = 1;
    rep(i, max_index)
    {
        if (num[i] == 0)
        {
            ans = 0;
            break;
        }
        rep(j, num[i + 1])
        {
            ans *= num[i];
        }
    }
    cout << ans.get() << endl;
}

int main()
{
    std::cin.tie(nullptr);
    std::ios_base::sync_with_stdio(false);
    std::cout << std::fixed << std::setprecision(15);
    Main();
    return 0;
}


Measured memory_bytes: 1024