#include <bits/stdc++.h>
#include <atcoder/all>
using namespace std;
using namespace atcoder;
#define ll long long
#define rep(i,a,b) for(int i=(a);i<(b);i++)
#define repl(i,a,b) for(ll i=(a);i<(b);i++)
#define all(a) (a).begin(),(a).end()
#define rall(a) (a).rbegin(),(a).rend()

template <typename T> bool chmin(T &a,T b){if(a>b){a=b;return true;} return false;}
template <typename T> bool chmax(T &a,T b){if(a<b){a=b;return true;} return false;}


ll mod=998244353;
// ll mod=1000000007;
using mint=modint998244353;
int MAX=1e6;
vector<mint> fac(MAX),inv(MAX),finv(MAX);
void COMinit(){
  fac[0]=fac[1]=1;
  inv[1]=1;
  finv[0]=finv[1]=1;
  rep(i,2,MAX){
    fac[i]=fac[i-1]*i;
    inv[i]=-(mod/i)*inv[mod%i];
    finv[i]=finv[i-1]*inv[i];
  }
  return;
}

mint COM(ll n,ll k){
  if(n<k || n<0 || k<0) return 0;
  return (fac[n]*finv[k])*finv[n-k];
}

void solve(){
  COMinit();
  int n; cin >> n;
  vector<int> a(n);
  rep(i,0,n) cin >> a[i], a[i]--;
  int x=n-1,y=0;
  mint ans=0;
  while(y<=a[0]){
    if(a[x] == y){
      if(x<n-1 && a[x+1] == a[x]) ans+=COM(x+y,y);
      else ans+=2*COM(x+y,y);
      x--;
      if(x>=0 && a[x]>y) y++;
    }
    else{
      ans+=COM(x+y,y);
      y++;
    }
  }
  cout << ans.val() << "\n";

  return;
}
  
int main(){
  ios::sync_with_stdio(false);
  cin.tie(nullptr);

  int T=1;
  // cin >> T;
  rep(_,0,T){
    solve();
  }
}