#include <bits/stdc++.h>
using namespace std;
using ll = long long;
using P = pair<ll,ll>;
#define fix(x) fixed << setprecision(x)
#define asc(x) x, vector<x>, greater<x>
#define rep(i, n) for(ll i = 0; i < n; i++)
#define all(x) (x).begin(),(x).end()
template<class T>bool chmin(T&a, const T&b){if(a>b){a=b;return 1;}return 0;}
template<class T>bool chmax(T&a, const T&b){if(a<b){a=b;return 1;}return 0;}
const ll MOD = 998244353;
int main(){
    cin.tie(nullptr);
    ios::sync_with_stdio(false);
    int n;
    cin >> n;
    vector<ll> a(n), t2(n+1);
    t2[0] = 1;
    rep(i,n){
        cin >> a[i];
        t2[i+1] = t2[i] * 2 % MOD;
    }
    ll x = 0, y = 0, ans = 0;
    rep(i,n-1){
        x = x + a[i] % MOD;
        y = y + a[n-i-1] % MOD;
        ans = (ans + (x - y) * t2[n-2-i]) % MOD;
    }
    cout << (ans + MOD) % MOD << '\n';
    return 0;
}