#include <bits/stdc++.h>
#include <atcoder/all>
using mint = atcoder::static_modint<998244353>;
//using mint = atcoder::static_modint<1000000007>;
using namespace std;
using namespace atcoder;
using ld = long double;
using ll = long long;
#define mp(a,b) make_pair(a,b)
#define rep(i,s,n) for(int i=s; i<n; i++)


vector<mint> factorial(200005,1),invfactorial(200005,1);
mint combo(int n,int r){
    if(n>=r && r>=0)return factorial[n]*invfactorial[n-r]*invfactorial[r];
    return 0;
}
int main(){
    int n;
    cin >> n;
    vector<int> a(n);
    rep(i,1,200005)factorial[i]=factorial[i-1]*i,invfactorial[i]=factorial[i].inv();
    rep(i,0,n)cin >> a[n-1-i];
    mint ans=0;
    int k=1;
    rep(i,0,n){
        while(k<=a[i]){
            ans+=combo(n-1-i+k-1,k-1);
            k++;
        }
        ans+=combo(n-1-i+a[i]-1,a[i]-1);
    }
    cout << ans.val();
}