import sys
input = lambda: sys.stdin.readline().rstrip()
import math, random
from bisect import bisect_right, bisect_left
from itertools import product, permutations, combinations, combinations_with_replacement 
from collections import deque, defaultdict, Counter
from heapq import heapify, heappush, heappop
from functools import lru_cache, reduce
inf = float('inf')
def error(*args, sep=' ', end='\n'):
  print(*args, sep=sep, end=end, file=sys.stderr)
def ltos(a, f=str, sep=' '):
  return sep.join(map(f, a))
# mod = 1000000007
mod = 998244353
# sys.setrecursionlimit(10**6)

#  -----------------------  #

n = int(input())
A = list(map(int, input().split()))

cnt = pow(2, n-1, mod)-1
ans = A[0] * cnt
ans -= A[-1] * cnt
print(ans % mod)