// include
// ------------------------------------------------
#include <bits/stdc++.h>
#include <math.h>

using namespace std;

// func
// ------------------------------------------------
int CalcSumOfDigit(int n);      // 各桁の和を計算する。
int getDigit(int n);            // 数字の桁数を取得する。
string upper(string str);       // 英字を大文字に変換する。
string lower(string str);       // 英字を小文字に変換する。
vector<pair<long long,long long>> prime_factorize(long long p); // 素因数分解

// class
// ------------------------------------------------
class Combi {
  public:
    Combi();
    long long Combination(long long n, long long k);
    long long nPk_modp(long long n, long long k, long long p);
  private:
    vector<vector<long long>> memo;
    long long n_num;
    long long k_num;
    void Resize(long long n, long long k);
};

// define
// ------------------------------------------------
#define all(a)        (a).begin(),(a).end()
#define rall(a)       (a).rbegin(),(a).rend()
#define sz(a)         int((a).size())
#define rep(i,n)      for(int(i)=0;(i)<(n);(i)++)
#define repe(i,n)     for(int(i)=0;(i)<=(n);(i)++)
#define vsort(v)      sort((v).begin(),(v).end())
#define rvsort(v)     sort(rall((v)))
#define vi            vector<int>
#define GCD(a,b)      __gcd((a),(b))
#define LCM(a,b)      (a)/GCD((a),(b))*(b)
#define kiriage(a,b)  ((a)+(b)-1)/(b)

const int INF = 1e9;

typedef long long ll;
typedef unsigned long long ull;
typedef vector<long> vll;
// code
// ------------------------------------------------
int main() {

    ull mo = 998244353;

    ull n;
    cin >> n;
    vll d(n);

    map<ull,ull> m;

    rep(i,n) {
        cin >> d[i];
        m[d[i]]++;
    }

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

    ull ans = 1;
    ull bef_val = m.begin() -> first;
    ull bef_num = m.begin() -> second;

    if(bef_val != 0 || bef_num != 1) {
        cout << 0 << endl;
        return 0;
    }

    for(auto it : m){
        if(it.first == 0)
            continue;
        
        if(m[it.first - 1] != 0) {
            ull sub = 1;
            rep(i,it.second) {
                sub = (sub * bef_num) % mo;
            }
            ans = ans * sub % mo;
            bef_val = it.first;
            bef_num = it.second;
        } else {
            cout << 0 << endl;
            return 0;
        }
    }

    cout << ans << endl;

    return 0;
}
// funcの実体
// ------------------------------------------------
int getDigit(int n) {
  int i = 1;
  while(1) {
    n = n / 10;
    if(n == 1)
      break;
    i++;
  }
  return i;
}
int CalcSumOfDigit(int n) {
  int s = 0;
  while(n) {
    s += n % 10;
    n = n / 10;
  }
  return s;
}

string upper(string str) {
  for(auto itr = str.begin();itr != str.end() ; itr++) {
    if(97 <= *itr && *itr <= 122) {
      *itr = *itr - 32;
    }
  }
  return str;
}

string lower(string str) {
  for(auto itr = str.begin();itr != str.end() ; itr++) {
    if(65 <= *itr && *itr <= 90) {
      *itr = *itr + 32;
    }
  }
  return str;
}


Combi::Combi() {
  n_num = -1;
  k_num = -1;
};
ll Combi::Combination(ll n, ll k) {
  Resize(n,k);

  ll ret;
  if(memo[n][k] != 0) {
    ret = memo[n][k];
  } else if(n == k || k == 0) {
    memo[n][k] = 1;
    ret = 1;
  } else {
    ret = Combination(n - 1, k - 1) + Combination(n - 1, k);
    memo[n][k] = ret;
  }
  return ret;
}

void Combi::Resize(ll n, ll k) {
  if(n_num <= n || k_num <= k) {
    n_num = (n + 1) * 2;
    k_num = (k + 1) * 2;
    memo.resize(n_num);
    for(auto itr = memo.begin(); itr != memo.end(); ++itr) {
      itr->resize(k_num);
    }
  }
}

long long Combi::nPk_modp(long long n, long long k, long long p) {
  ll ans = 1;
  for(long long i = k; i <= n; i++) {
    ans = (ans * i) % p;
  }

  return ans;
};

vector<pair<long long,long long>> prime_factorize(long long p) {
    vector<pair<long long,long long>> ret;

    for(long long x = 2; x * x <= p; ++x) {
        if(p % x != 0) continue;
        long long num = 0;
        while(p % x == 0) {
            num++;
            p /= x;
        }
        ret.push_back(make_pair(x,num));
    }

    if(p != 1) ret.push_back(make_pair(p, 1));
    
    return ret;
}

Measured memory_bytes: 7296