#include<bits/stdc++.h>
namespace {
#pragma GCC diagnostic ignored "-Wunused-function"
#include<atcoder/all>
#pragma GCC diagnostic warning "-Wunused-function"
using namespace std;
using namespace atcoder;
#define rep(i,n) for(int i = 0; i < (int)(n); i++)
#define rrep(i,n) for(int i = (int)(n) - 1; i >= 0; i--)
#define all(x) begin(x), end(x)
#define rall(x) rbegin(x), rend(x)
template<class T> bool chmax(T& a, const T& b) { if (a < b) { a = b; return true; } else return false; }
template<class T> bool chmin(T& a, const T& b) { if (b < a) { a = b; return true; } else return false; }
using ll = long long;
using P = pair<int,int>;
using VI = vector<int>;
using VVI = vector<VI>;
using VL = vector<ll>;
using VVL = vector<VL>;
using mint = modint998244353;

template <class T>
struct cntsum {
  T a, b;  // a+bx mod x^2
  friend cntsum operator+(const cntsum& lhs, const cntsum& rhs) { return {lhs.a + rhs.a, lhs.b + rhs.b}; }
  friend cntsum operator-(const cntsum& lhs, const cntsum& rhs) { return {lhs.a - rhs.a, lhs.b - rhs.b}; }
  friend cntsum operator*(const cntsum& lhs, const cntsum& rhs) { return {lhs.a * rhs.a, lhs.a * rhs.b + lhs.b * rhs.a}; }
  friend cntsum operator*(const T& c, const cntsum& x) { return {x.a, x.b + c * x.a}; }
  cntsum& operator+=(const cntsum& x) { return *this = *this + x; }
  cntsum& operator-=(const cntsum& x) { return *this = *this - x; }
  cntsum& operator*=(const cntsum& x) { return *this = *this * x; }
};

using CS = cntsum<mint>;

} int main() {
  ios::sync_with_stdio(false);
  cin.tie(0);
  int x;
  cin >> x;
  CS d{1, 0};
  mint ans;
  const mint inv2 = mint(2).inv();
  const mint inv6 = mint(6).inv();
  rep(_, x) {
    int yi;
    cin >> yi;
    mint y = yi;
    ans += (y - 1) * y * (y + 1) * inv6;
    CS nd{y, y * (y + 1) * inv2};
    ans += (d * nd).b;
    d += nd;
  }
  cout << ans.val() << '\n';
}