#include <bits/stdc++.h>
using namespace std;
#if __has_include(<atcoder/all>)
#include <atcoder/all>
using namespace atcoder;
template<int mod>istream &operator>>(istream &is,static_modint<mod> &a){long long b;is>>b;a=b;return is;}
istream &operator>>(istream &is,modint &a){long long b;cin>>b;a=b;return is;}
#endif
#ifdef LOCAL
#include "debug.h"
#else
#define debug(...) static_cast<void>(0)
#define debugg(...) static_cast<void>(0)
#define esper(...) static_cast<void>(0)
template<typename T1,typename T2>ostream &operator<<(ostream &os,const pair<T1,T2>&p){os<<p.first<<' '<<p.second;return os;}
#endif
using ll=long long;
using ull=unsigned long long;
using P=pair<ll,ll>;
template<typename T>using minque=priority_queue<T,vector<T>,greater<T>>;
template<typename T>bool chmax(T &a,const T &b){return (a<b?(a=b,true):false);}
template<typename T>bool chmin(T &a,const T &b){return (a>b?(a=b,true):false);}
template<typename T1,typename T2>istream &operator>>(istream &is,pair<T1,T2>&p){is>>p.first>>p.second;return is;}
template<typename T>istream &operator>>(istream &is,vector<T> &a){for(auto &i:a)is>>i;return is;}
template<typename T1,typename T2>void operator++(pair<T1,T2>&a,int n){a.first++,a.second++;}
template<typename T1,typename T2>void operator--(pair<T1,T2>&a,int n){a.first--,a.second--;}
template<typename T>void operator++(vector<T>&a,int n){for(auto &i:a)i++;}
template<typename T>void operator--(vector<T>&a,int n){for(auto &i:a)i--;}
#define reps(i,a,n) for(int i=(a);i<int(n);i++)
#define rep(i,n) reps(i,0,n)
#define all(x) x.begin(),x.end()
#define pcnt(x) __builtin_popcountll(x)
#define fin(x) return cout<<x<<'\n',static_cast<void>(0)
ll myceil(ll a,ll b){return (a+b-1)/b;}
template<typename T,size_t n,size_t id=0>
auto vec(const int (&d)[n],const T &init=T()){
  if constexpr (id<n)return vector(d[id],vec<T,n,id+1>(d,init));
  else return init;
}
void SOLVE();
int main(){
  ios::sync_with_stdio(false);
  cin.tie(nullptr);
  cout<<fixed<<setprecision(16);
  #ifdef LOCAL
  clock_t start=clock();
  #endif
  int testcase=1;
  //cin>>testcase;
  for(int i=0;i<testcase;i++){
    SOLVE();
  }
  #ifdef LOCAL
  cerr<<"time:";
  cerr<<(clock()-start)/1000;
  cerr<<"ms\n";
  #endif
}
template<typename T>
struct factorial_table{
private:
  int mod,capacity;
  vector<T>fact,factinv,inv;
  void resize(int n){
    fact.resize(n+1),factinv.resize(n+1),inv.resize(n+1);
    for(int i=capacity+1;i<=n;i++){
      fact[i]=fact[i-1]*i;
      inv[i]=-inv[mod%i]*(mod/i);
      factinv[i]=factinv[i-1]*inv[i];
    }
    capacity=n;
  }
public:
  factorial_table():capacity(1),mod(T::mod()),fact{1,1},factinv{1,1},inv{0,1}{}
  T C(int n,int k){
    if(n<k)return 0;
    if(k<0)return 0;
    if(capacity<n)resize(n);
    return fact[n]*factinv[k]*factinv[n-k];
  }
  T P(int n,int k){
    if(n<k)return 0;
    if(k<0)return 0;
    if(capacity<n)resize(n);
    return fact[n]*factinv[n-k];
  }
  T H(int n,int k){
    return C(n+k-1,k);
  }
  T factorial(int n){
    if(capacity<n)resize(n);
    return fact[n];
  }
  T S(ll n,int k){
    if(n<0)return 0;
    if(n<k)return 0;
    T ret=0;
    if(capacity<k)resize(k);
    rep(i,k+1){
      ret+=fact[k]*factinv[i]*factinv[k-i]*T::raw(i).pow(n)*((k-i)&1?-1:1);
    }
    return ret*factinv[k];
  }
  template<typename... INT>
  T O(INT...k){
    int n=0;
    for(int i:initializer_list<int>{k...}){
      if(i<0)return 0;
      n+=i;
    }
    if(capacity<n)resize(n);
    T ret=fact[n];
    for(int i:initializer_list<int>{k...})ret*=factinv[i];
    return ret;
  }
};
using mint=modint998244353;
factorial_table<mint>table;
void SOLVE(){
  int n;
  cin>>n;
  vector<int>a(n);
  cin>>a;
  if(reduce(all(a))&1)fin(0);
  string s=string(a[0],'1')+'0';
  reps(i,1,n){
    s+=string(a[i]-a[i-1],'1');
    s+='0';
  }
  string l,r;
  rep(i,s.size()){
    (i&1?l:r)+=s[i];
  }
  vector<int>b,c;
  auto f=[](string s)->vector<int> {
    vector<int>a;
    int cnt=0;
    rep(i,s.size()){
      if(s[i]=='1')cnt++;
      else{
        a.push_back(cnt);
      }
    }
    return a;
  };
  b=f(l),c=f(r);
  auto calc=[](vector<int>a)->mint {
    mint ret=1;
    fenwick_tree<int>BIT(1001);
    rep(i,a.size()){
      reps(j,1,a[i]+1){
        ret*=BIT.sum(j,1001)+a[i]-j+1;
      }
      BIT.add(a[i],1);
    }
    return table.factorial(reduce(all(a)))/ret;
  };
  int as=reduce(all(b)),bs=reduce(all(c));
  if((as+bs)*2!=reduce(all(a)))fin(0);
  cout<<(table.C(as+bs,as)*calc(b)*calc(c)).val()<<endl;
}