#if __INCLUDE_LEVEL__ == 0

#include __BASE_FILE__

namespace {

using Mint = atcoder::modint998244353;

Comb<Mint> comb(1e6);

void solve() {
  Int n;
  scan(n);
  Vec<Int> a(n);
  scan(a);
  Vec<Pair<Int, Int>> v;
  for (i : rep(n + 1)) {
    if (i == 0) {
      v.emplace_back(i, a[i]);
    } else if (i == n) {
      for (j : rev(rep(a.back() + 1))) {
        v.emplace_back(i, j);
      }
    } else {
      for (j : rev(rep1(a[i], a[i - 1]))) {
        v.emplace_back(i, j);
      }
    }
  }
  ranges::sort(v);
  Mint ans = 0;
  for ([i, j] : v) {
    ans += comb.binom(i + j, i);
    if (ranges::binary_search(v, Pair{i + 1, j})) {
      ans -= comb.binom(i + j, i);
    }
    if (ranges::binary_search(v, Pair{i, j + 1})) {
      ans -= comb.binom(i + j, i);
    }
  }
  print(ans);
}

}  // namespace

int main() {
  std::ios::sync_with_stdio(false);
  std::cin.tie(nullptr);
  std::cout << std::setprecision(std::numeric_limits<Float>::max_digits10);

  solve();
}

#else  // __INCLUDE_LEVEL__

#include <bits/stdc++.h>

#include <atcoder/modint>

template <class T>
std::vector<T> make_vector_for_overwrite(int n) {
  static_assert(std::is_trivially_destructible_v<T>);
  std::vector<T> v;
  static_assert(sizeof(v) == 3 * sizeof(T*));
  v.reserve(n);
  T*(&a)[3] = reinterpret_cast<T*(&)[3]>(v);
  assert(a[0] == a[1] && a[1] + n == a[2]);
  a[1] = a[2];
  return v;
}

template <class T>
class Comb {
 public:
  Comb() = default;

  explicit Comb(int max_n)
      : fact_(make_vector_for_overwrite<T>(max_n + 1)),
        recip_fact_(make_vector_for_overwrite<T>(max_n + 1)) {
    fact_[0] = 1;
    for (const int n : std::views::iota(1, max_n + 1)) {
      fact_[n] = fact_[n - 1] * n;
    }
    recip_fact_[max_n] = 1 / fact_[max_n];
    for (const int n : std::views::iota(1, max_n + 1) | std::views::reverse) {
      recip_fact_[n - 1] = n * recip_fact_[n];
    }
  }

  T recip(int n) const {
    assert(n);
    return n < 0 ? -recip(-n) : recip_fact_[n] * fact_[n - 1];
  }

  T fact(int n) const {
    assert(0 <= n);
    return fact_[n];
  }

  T recip_fact(int n) const { return n < 0 ? 0 : recip_fact_[n]; }

  T falling_fact(int n, int k) const {
    assert(0 <= n || n < k);
    if (n < 0) {
      const T t = falling_fact(k - n - 1, k);
      return k & 1 ? -t : t;
    }
    return n < k ? 0 : recip_fact(n - k) * fact(n);
  }

  T recip_falling_fact(int n, int k) const {
    assert(n < 0 || k <= n);
    return falling_fact(n - k, -k);
  }

  T rising_fact(int n, int k) const {
    assert(n <= 0 || 0 < n + k);
    return falling_fact(n + k - 1, k);
  }

  T recip_rising_fact(int n, int k) const {
    assert(0 < n || n + k <= 0);
    return falling_fact(n - 1, -k);
  }

  T binom(int n, int k) const {
    if ((n < 0) ^ (k < 0) ^ (n < k)) {
      return 0;
    }
    if (n < 0 && k < 0) {
      k = n - k;
    }
    return recip_fact(k) * falling_fact(n, k);
  }

  T recip_binom(int n, int k) const {
    assert((0 <= n) ^ (0 <= k) ^ (k <= n));
    k = std::max(k, n - k);
    return recip_falling_fact(n, k) * fact(k);
  }

  T multiset(int n, int k) const { return binom(n + k - 1, k); }

  T recip_multiset(int n, int k) const {
    assert((0 < n) ^ (0 <= k) ^ (0 < n + k));
    return recip_binom(n + k - 1, k);
  }

 private:
  std::vector<T> fact_;
  std::vector<T> recip_fact_;
};

using Int = int64_t;
using Float = double;
using Str = std::string;

template <class T1, class T2>
using Pair = std::pair<T1, T2>;

template <class... Ts>
using Tuple = std::tuple<Ts...>;

template <class T, size_t N>
using Arr = std::array<T, N>;

template <class T>
using Vec = std::vector<T>;

template <class T>
using Set = std::set<T>;

template <class T>
using Multiset = std::multiset<T>;

template <class K, class T>
using Map = std::map<K, T>;

template <class T>
using MinHeap = std::priority_queue<T, Vec<T>, std::greater<T>>;

template <class T>
using MaxHeap = std::priority_queue<T>;

namespace ranges = std::ranges;
namespace views = std::views;

inline constexpr auto len = ranges::ssize;
inline constexpr auto rev = views::reverse;

constexpr auto rep(Int l, Int r) { return views::iota(std::min(l, r), r); }
constexpr auto rep(Int n) { return rep(0, n); }
constexpr auto rep1(Int l, Int r) { return rep(l, r + 1); }
constexpr auto rep1(Int n) { return rep(1, n + 1); }

template <class T, class U = T>
bool chmin(T& x, U&& y) {
  return y < x && (x = std::forward<U>(y), true);
}

template <class T, class U = T>
bool chmax(T& x, U&& y) {
  return x < y && (x = std::forward<U>(y), true);
}

template <std::signed_integral T = Int>
T inf() {
  T ret;
  std::memset(&ret, 0x3f, sizeof(ret));
  return ret;
}

template <std::floating_point T>
T inf() {
  return std::numeric_limits<T>::infinity();
}

template <class T>
concept Range = ranges::range<T> && !std::convertible_to<T, std::string_view>;

template <class T>
concept TupleLike = std::__is_tuple_like<T>::value && !Range<T>;

namespace std {

istream& operator>>(istream& is, Range auto&& r) {
  for (auto&& e : r) {
    is >> e;
  }
  return is;
}

istream& operator>>(istream& is, TupleLike auto&& t) {
  return apply([&](auto&... xs) -> istream& { return (is >> ... >> xs); }, t);
}

ostream& operator<<(ostream& os, Range auto&& r) {
  for (string_view sep = ""; auto&& e : r) {
    os << exchange(sep, " ") << e;
  }
  return os;
}

ostream& operator<<(ostream& os, TupleLike auto&& t) {
  const auto f = [&](auto&... xs) -> ostream& {
    [[maybe_unused]] string_view sep = "";
    ((os << exchange(sep, " ") << xs), ...);
    return os;
  };
  return apply(f, t);
}

template <class T, atcoder::internal::is_modint_t<T>* = nullptr>
istream& operator>>(istream& is, T& x) {
  int v;
  is >> v;
  x = T::raw(v);
  return is;
}

template <class T, atcoder::internal::is_modint_t<T>* = nullptr>
ostream& operator<<(ostream& os, const T& x) {
  return os << x.val();
}

}  // namespace std

#define DEF_INC_OR_DEC(op) \
  auto& operator op(Range auto&& r) { \
    for (auto&& e : r) { \
      op e; \
    } \
    return r; \
  } \
  auto& operator op(TupleLike auto&& t) { \
    std::apply([](auto&... xs) { (op xs, ...); }, t); \
    return t; \
  }

DEF_INC_OR_DEC(++)
DEF_INC_OR_DEC(--)

#undef DEF_INC_OR_DEC

void scan(auto&&... xs) { std::cin >> std::tie(xs...); }
void print(auto&&... xs) { std::cout << std::tie(xs...) << '\n'; }

template <class F>
class fix {
 public:
  explicit fix(F f) : f_(std::move(f)) {}

  decltype(auto) operator()(auto&&... xs) const {
    return f_(std::ref(*this), std::forward<decltype(xs)>(xs)...);
  }

 private:
  F f_;
};

#define for(...) for ([[maybe_unused]] auto&& __VA_ARGS__)

#endif  // __INCLUDE_LEVEL__