#include<bits/stdc++.h>
using namespace std;
#define ll long long int
#define me BOSS
#define bug() cout<<"AIkahne aise"<<endl
ll A[5000001],bin[5000001];
vector<ll>v;
map<int,int>myMap;
set<int>mySet;
vector<pair<ll,ll> >vp;
/* Precode Start Here *\



     Sieve
void sieve()
{
    for(ll i=3; i<=2000; i+=2)
    {
        for(ll j=i*i; j<=4000000; j+=i)
            A[j]=1;
    }
    v.push_back(2);
    for(ll i=3; i<=4000000; i+=2)
        if(A[i]==0)
            v.push_back(i);
}

     Power Function Modulo P

ll modPow(ll a, ll x, ll p) {
    //calculates a^x mod p in logarithmic time.
    long res = 1;
    while(x > 0) {
        if( x % 2 != 0) {
            res = (res * a) % p;
        }
        a = (a * a) % p;
        x /= 2;
    }
    return res;
}


   factorial

ll fact(ll n)
{
    ll ans=1;
    for(ll i=1;i<=n;i++)
    {
        ans=(ans*i)%mod;
    }
    return ans;
}
     Calculating nCr using Fermats law Theorem

ll modInverse(ll a, ll p) {
    //calculates the modular multiplicative of a mod m.
    //(assuming p is prime).
    return modPow(a, p-2, p);
}


ll modBinomial(ll n, ll k, ll p) {
// calculates C(n,k) mod p (assuming p is prime).

    ll numerator = 1; // n * (n-1) * ... * (n-k+1)
    for (ll i=0; i<k; i++) {
        numerator = (numerator * (n-i) ) % p;
    }

    ll denominator = 1; // k!
    for (ll i=1; i<=k; i++) {
        denominator = (denominator * i) % p;
    }

    // numerator / denominator mod p.
    return ( numerator* modInverse(denominator,p) ) % p;
}
     num of divisor and euler totient

ll phi[1000001],mark[1000001],divi[1000001];;
void divisorPhi(ll n)
{
    for(int i=1;i<=n;i++)
        phi[i]=i;
    for(int i=2;i<=n;i++)
    {
        if(!mark[i])
        {
            for(int j=i;j<=n;j+=i)
            {
                mark[j]=1;
                phi[j]*=(1-1/(double)i);
            }
        }
    }
    for(ll i=1;i<=n;i++)
    {
        for(ll j=i;j<=n;j+=i)
            divi[j]++;
    }
}




/* Precode Ends */
#define mod 998244353
ll modPow(ll a, ll x, ll p) {
    //calculates a^x mod p in logarithmic time.
    long res = 1;
    while(x > 0) {
        if( x % 2 != 0) {
            res = (res * a) % p;
        }
        a = (a * a) % p;
        x /= 2;
    }
    return res;
}

ll modInverse(ll a, ll p) {
    //calculates the modular multiplicative of a mod m.
    //(assuming p is prime).
    return modPow(a, p-2, p);
}


ll modBinomial(ll n, ll k, ll p) {
// calculates C(n,k) mod p (assuming p is prime).

    ll numerator = 1; // n * (n-1) * ... * (n-k+1)
    for (ll i=0; i<k; i++) {
        numerator = (numerator * (n-i) ) % p;
    }

    ll denominator = 1; // k!
    for (ll i=1; i<=k; i++) {
        denominator = (denominator * i) % p;
    }

    // numerator / denominator mod p.
    return ( numerator* modInverse(denominator,p) ) % p;
}
int main()
{
ios::sync_with_stdio(false);
cin.tie(nullptr);
 ll n,ans=1,f=0;
 cin>>n;
 for(int i=0;i<n;i++)
 {
     cin>>A[i];
     mySet.insert(A[i]);
     myMap[A[i]]++;
     if(i==0)
     {
         if(A[i]!=0)
         {
             f=1;
         }
     }
 }
 v.assign(mySet.begin(),mySet.end());
 //cout<<v[0]<<endl;
 if(v[0]!=0||myMap[0]>1||f==1)
 {
     cout<<0<<endl;
     return 0;
 }
 for(int i=0;i<v.size()-1;i++)
 {
     if(v[i+1]-v[i]>1)
     {
         cout<<0<<endl;
         return 0;
     }
 }
 for(int i=v.size()-1;i>0;i--)
 {
     ll p=myMap[v[i]];
     ll q=myMap[v[i-1]];
     //cout<<v[i]<<" "<<v[i-1]<<" "<<p<<" "<<q<<endl;
     //cout<<p<<" "<<q<<endl;
     if(q>1)
     ans= ((ans%mod)*modPow(q,p,mod))%mod;
 }
 cout<<ans<<endl;
return 0;
}



Measured memory_bytes: 12416