#include <iostream>
#include <vector>
#include <algorithm>
#include <cmath>
#include <bits/stdc++.h>
#include <atcoder/all>
using namespace std;
using namespace atcoder;
using ll = long long;
using mint = modint998244353;
using vi = vector<int>;
using vvi = vector<vi>;
using vvvi = vector<vvi>;
using vll = vector<ll>;
using vvll = vector<vll>;
using vvvll = vector<vvll>;
using vmi = vector<mint>;
using vvmi = vector<vmi>;
using vvvmi = vector<vvmi>;
#define all(a) (a).begin(), (a).end()
#define rep2(i, m, n) for (int i = (m); i < (n); ++i)
#define rep(i, n) rep2(i, 0, n)
#define drep2(i, m, n) for (int i = (m)-1; i >= (n); --i)
#define drep(i, n) drep2(i, n, 0)

void solve(){
    
}
mint sum(ll n, ll k){
    return mint(n)*mint(k)*mint(k+1)/mint(2) - mint(k)*mint(k+1)*mint(2*k+1)/mint(6);
}

int main(){

    int x; cin >> x;
    vll y(x); ll s = 1; rep(i, x){
        cin >> y[i];
        s += y[i];
    }
    mint ans = 0;
    rep(i, x){
        ans += sum(s, y[i]);
    }cout << ans.val() << endl;
    return 0;
}