#include <bits/stdc++.h>
#include <atcoder/all>
using namespace std;
using namespace atcoder;
using ll = long long;
using ld = long double;
using mint = modint998244353;
istream& operator>> (istream& is, mint& x) { long long x_; is >> x_; x = x_; return is; }
ostream& operator<< (ostream& os, const mint& x) { os << x.val(); return os; }
#define int ll
#define OVERLOAD_REP(_1, _2, _3, name, ...) name
#define REP2(i, l, r) for (int i = (int)(l); i < (int)(r); ++i)
#define REP1(i, n) REP2(i, 0, n)
#define rep(...) OVERLOAD_REP(__VA_ARGS__, REP2, REP1)(__VA_ARGS__)
#define RREP2(i, r, l) for (int i = (int)(r)-1; i >= (int)(l); --i)
#define RREP1(i, n) RREP2(i, n, 0)
#define rrep(...) OVERLOAD_REP(__VA_ARGS__, RREP2, RREP1)(__VA_ARGS__)
#define all(x) begin(x), end(x)
#define rall(x) rbegin(x), rend(x)
#define debug(x) cerr << #x << ": " << (x) << endl
#define pb push_back
#define mp make_pair
#define mt make_tuple
const int INF = 4e18;
const int MOD = 998244353;
const int MOD1 = 1e9 + 7;
template<class T> inline bool chmax(T &a, T b) { return a < b ? a = b, 1 : 0; }
template<class T> inline bool chmin(T &a, T b) { return a > b ? a = b, 1 : 0; }
template<class T> T pow(T a, T b, T m) { return b ? b&1 ? a*pow(a, b^1, m)%m : pow(a*a%m, b>>1, m)%m : 1; }
template<class T> T pow(T a, T b) { return b ? b&1 ? pow(a, b^1)*a : pow(a*a, b>>1) : 1; }
template<class... T> void input(T&... args) { ((cin >> args), ...); }
template<class... T> void print(T... args) { ((cout << args << " "), ...); }
template<class... T> void println(T... args) { print(args...); cout << endl; }
template<class T> void println(vector<T> A) { for (T a : A) print(a); cout << endl; }

mint comb(int n, int r) {
    static map<pair<int, int>, mint> memo;
    if (r < 0 || n < r) return 0;
    chmin(r, n-r);
    if (r == 0) return 1;
    if (memo.count(mp(n, r)) == 0) memo[mp(n, r)] = comb(n-1, r-1) + comb(n-1, r);
    return memo[mp(n, r)];
}

mint multi_comb(int n, int r) {
    return comb(n+r-1, r);
}

signed main() {
    ios::sync_with_stdio(false);
    cin.tie(nullptr);
    
    int N;
    input(N);
    vector<int> A(N);
    rep(i, N) input(A[i]);
    A.pb(0);
    
    mint ans = 0;
    rep(i, N) {
    	ans += comb(i + A[i] - 1, i);
    	rep(j, A[i+1], A[i]) ans += comb(i + j, i);
    }
    println(ans);
}