#include <bits/stdc++.h>

using namespace std;

typedef long long ll;
typedef pair<ll, ll> P;
typedef pair<int, int> Pi;
typedef vector<ll> Vec;
typedef vector<int> Vi;
typedef vector<string> Vs;
typedef vector<vector<ll>> VV;

#define REP(i, a, b) for(ll i=(a); i<(b); i++)
#define rep(i, n) REP(i, 0, n)
const ll INF=1e9;
const ll MAX=100005;
const ll MOD=998244353;
#define Yes(n) cout << ((n) ? "Yes" : "No") << endl;
#define YES(n) cout << ((n) ? "YES" : "NO") << endl;
#define ALL(v) v.begin(), v.end()
#define pb(x) push_back(x)
#define mp(a, b) make_pair(a,b)
#define Each(a,b) for(auto &a :b)
#define REPM(i, mp) for (auto i = mp.begin(); i != mp.end(); ++i)
#define dbg(x_) cerr << #x_ << ":" << x_ << endl;
#define dbgmap(mp) cerr << #mp << ":"<<endl; for (auto i = mp.begin(); i != mp.end(); ++i) { cerr << i->first <<":"<<i->second << endl;}
#define dbgarr(n,m,arr) rep(i,n){rep(j,m){cerr<<arr[i][j]<<" ";}cerr<<endl;}
#define dbgdp(n,arr) rep(i,n){cerr<<arr[i]<<" ";}cerr<<endl;
#define sum(v) accumulate(ALL(v),0)
#define fi first
#define se second

template<typename T1, typename T2>
ostream &operator<<(ostream &s, const pair<T1, T2> &p) { return s<<"("<<p.first<<", "<<p.second<<")"; }

// vector
template<typename T>
ostream &operator<<(ostream &s, const vector<T> &v) {
    int len=v.size();
    for(int i=0; i<len; ++i) {
        s<<v[i];
        if(i<len-1) s<<"	";
    }
    return s;
}

// 2 dimentional vector
template<typename T>
ostream &operator<<(ostream &s, const vector<vector<T> > &vv) {
    int len=vv.size();
    for(int i=0; i<len; ++i) {
        s<<vv[i]<<endl;
    }
    return s;
}


struct mint {
    ll x; // typedef long long ll;
    mint(ll x=0):x((x%MOD+MOD)%MOD){}
    mint& operator+=(const mint a) {
        if ((x += a.x) >= MOD) x -= MOD;
        return *this;
    }
    mint& operator-=(const mint a) {
        if ((x += MOD-a.x) >= MOD) x -= MOD;
        return *this;
    }
    mint& operator*=(const mint a) {
        (x *= a.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(ll 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;
    }
};

ll pow_mod(ll n, ll k ,ll m){
    if(k==0){
        return  1;
    }else if(k%2 == 1){
        return pow_mod(n,k-1,m) * n % m;
    }else{
        ll t = pow_mod(n, k/2,m);
        return t*t % m;
    }
}


int main() {
    cin.tie(0);
    ios::sync_with_stdio(false);
    ll n;
    cin>>n;
    Vec d(n+1);
    rep(i,n){
        cin>>d[i];
    }
    if(d[0]!=0){
        cout<<0<<endl;
        return 0;
    }
    Vec cnt(n+1);
    rep(i,n){
        cnt[d[i]]++;
    }
    mint ans=1;

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

    ll chk=0;
    rep(i,n+1){
        if(i==0){
            continue;
        }
        if(cnt[i]==0){
            break;
        }
        ans *= pow_mod(cnt[i-1],cnt[i],MOD);
        chk+=cnt[i];
    }

    if(chk!=n-1){
        cout<<0<<endl;
        return 0;
    }
    cout<<ans.x<<endl;
    return  0;
}


Measured memory_bytes: 1792