import sys
input = sys.stdin.readline
from collections import *

N = int(input())
A = list(map(int, input().split()))
ans = 0
MOD = 998244353
p = [1]

for i in range(N+10):
    p.append(p[-1]*2%MOD)

for i in range(N):
    ans += p[N-1-i]*A[i]%MOD
    ans -= p[i]*A[i]%MOD
    ans %= MOD

print(ans)