#include <iostream>
#include <vector>
using namespace std;
const long long mod = 998244353;
int main(){
  int n;cin>>n;
  vector<long long> A(n);
  for(int i = 0; n > i; i++)cin>>A[i];
  vector<long long> B(n-1);
  long long sm = 0;
  for(int i = 0; n-1 > i; i++){
    B[i] = A[i]-A[i+1];
    sm = (sm + B[i])%mod;
  }
  long long tmp = sm;
  long long width = sm;
  long long nw = 1;
  long long ans = 0;
  for(int i = 0; n-1 > i; i++){
    ans = (ans + width * nw + mod)%mod;
    if((n-1)/2 >= i){
      tmp = (tmp - (B[i]+B[n-2-i]) + mod)%mod;
      width = (width+tmp)%mod;
    }else{
      width = (width-tmp+mod)%mod;
      tmp = (tmp+(B[i]+B[n-2-i]))%mod;
    }
    nw = (nw*2)%mod;
  }
  cout << ans << endl;
}