#include <bits/stdc++.h>
#define rep(i,n) for(int i=0;i<(n);++i)
using namespace std;
using ll = long long;

#include <atcoder/modint>
using mint = atcoder::modint998244353;

int main(){
    ios::sync_with_stdio(false);
    cin.tie(nullptr);
    
    int n;
    cin >> n;
    vector<int> a(n);
    rep(i,n) cin >> a[i];

    vector<mint> p(101010,1);
    rep(i,101010-1) p[i+1] *= p[i]*(i+1);

    mint ans = 1;

    rep(i,n){
        if(a[i]==1){
            ans += 1;
            continue;
        }
        int m = i+a[i]+1;
        int k = i+2;
        ans += p[m]/p[m-k]/p[k];
        ans -= p[m-1]/p[m-1-k]/p[k];
    }
    cout << ans.val() << endl;

}