#include <atcoder/modint>
#include <bits/stdc++.h>
using namespace std;
using ll = long long;
using mint = atcoder::modint998244353;
#define rep(i, n) for (int i = 0; i < (int)(n); i++)

const int MX = 200'010;
mint fact[MX + 10], finv[MX + 10];

mint c(ll a, ll b) {
  if (a < b || a < 0 || b < 0)
    return 0;
  return fact[a] * finv[a - b] * finv[b];
}

void solve() {
  fact[0] = finv[0] = 1;
  rep(i, MX) {
    fact[i + 1] = fact[i] * (i + 1);
    finv[i + 1] = fact[i + 1].inv();
  }
  ll n;
  cin >> n;
  vector<ll> a(n);
  rep(i, n) cin >> a[i];
  a.push_back(0);
  mint ans = 0;
  rep(i, n) {
    ans += c(a[i] - 1 + i, i);
    for (ll j = a[i]; j > a[i + 1]; j--)
      ans += c(j - 1 + i, i);
  }
  cout << ans.val() << '\n';
}

int main() {
  std::cin.tie(nullptr);
  std::ios_base::sync_with_stdio(false);
  int T = 1;
  for (int t = 0; t < T; t++) {
    solve();
  }
  return 0;
}