// #pragma GCC optimize ("Ofast") // #pragma GCC optimize ("unroll-loops") // #pragma GCC target ("avx,avx2,fma") #include using std::cin, std::cout, std::cerr; using ll = long long; const ll P = 998244353; ll Pow(ll a, ll b) { ll r = 1; for(; b; b /= 2) { if(b & 1) r = r * a % P; a = a * a % P; } return r; } ll Inv(ll x) { return Pow(x, P - 2); } struct Comb { std::vector inv, fac, ifac; Comb(int n) { Init(n); } void Init(int n) { inv.assign(n + 1, 0); fac.assign(n + 1, 0); ifac.assign(n + 1, 0); fac[0] = ifac[0] = 1; for(int i = 1; i <= n; i ++) { inv[i] = i == 1 ? 1 : (P - P / i) * inv[P % i] % P; fac[i] = fac[i - 1] * i % P; ifac[i] = ifac[i - 1] * inv[i] % P; } } ll Binom(int n, int m) { if(m < 0 || n < m) return 0; return fac[n] * ifac[m] % P * ifac[n - m] % P; } ll StirlingPartition(int n, int m) { ll ret = 0; for(int k = m; k >= 0; k --) { int sgn = (m - k) % 2 == 0 ? 1 : P - 1; ret += sgn * Binom(m, k) % P * Pow(k, n); ret %= P; } return ret * Inv(fac[m]) % P; } }comb(1e6 + 1); int main() { std::ios::sync_with_stdio(false); int n; cin >> n; std::vector a(n + 2); ll ans = 0; auto f = [](int x, int y) { return comb.Binom(x + y - 2, x - 1); }; for(int i = 1; i <= n; i ++) { cin >> a[i]; ans += f(i, a[i]); } for(int i = 1; i <= n; i ++) for(int j = a[i]; j > a[i + 1]; j --) ans += f(i, j); cout << ans % P << '\n'; }