//https://www.youtube.com/watch?v=Po8C2i6_ua4

#include <bits/stdc++.h>
#include <atcoder/all>
using namespace std;
using namespace atcoder;
#define rep(i, l, r) for (ll i = (l); i < (r); ++i)
#define all(x) (x).begin(), (x).end()
using ll = long long;
using pl = pair<ll,ll>;
using vl = vector<ll>;
using vvl = vector<vector<ll>>;
#pragma GCC target("avx2")
#pragma GCC optimize("O3")
#pragma GCC optimize("unroll-loops")
using mint=modint998244353;

int main(){
  ios::sync_with_stdio(false);
  cin.tie(nullptr);
  ll n;
  cin>>n;
  vl z(n);
  rep(i,0,n)cin>>z[i];
  ll r=0;
  rep(i,0,n){
    r+=z[i];
  }
  if(r>2*n){
    cout<<0<<endl;
    return 0;
  }
  vector<mint> bik(310000);
  vector<mint> gbik(310000);
  bik[0]=1;
  rep(i,0,300000){
    bik[i+1]=bik[i]*(i+1);
    gbik[i]=1/bik[i];
  }
  mint ans=1;
  stack<ll> s;
  rep(i,0,2*n+5)s.push(0);
  stack<ll> u;
  rep(i,0,2*n+5)u.push(0);
  stack<ll> d;
  rep(i,0,2*n+5)d.push(0);
  rep(i,0,n){
    z[i]+=2;
    ll p=0;
    while(s.top()==1){
        ans*=bik[i+1-u.top()-2]*gbik[i+1-d.top()-1]*gbik[d.top()-u.top()-1];
        p++;
        s.pop();
        u.pop();
        d.pop();
    }
    d.pop();
    d.push(i+1);
    s.pop();
    s.push(1);
    if(p+2>z[i]){
        cout<<0<<endl;
        return 0;
    }
    rep(j,0,z[i]-p-2){
        s.push(0);
        u.push(i+1);
        d.push(0);
    }
  }
  while(s.top()==1){
    ans*=bik[n+1-u.top()-2]*gbik[n+1-d.top()-1]*gbik[d.top()-u.top()-1];
    s.pop();
    u.pop();
    d.pop();
  }
  while(!s.empty()){
    if(s.top()==1){
        cout<<0<<endl;
        return 0;
    }
    s.pop();
  }
  cout<<ans.val()<<endl;
}