from re import A
import sys
#input = sys.stdin.readline
#input = sys.stdin.buffer.readline #文字列はダメ
#sys.setrecursionlimit(1000000)
#import math
import bisect
#import itertools
#import random
#from heapq import heapify, heappop, heappush
from collections import defaultdict
#from collections import deque
#import copy #DeepCopy: hoge = [_[:] for _ in hogehoge]
#from functools import lru_cache
#@lru_cache(maxsize=None)
#MOD = pow(10,9) + 7
MOD = 998244353
#dx = [1,0,-1,0]
#dy = [0,1,0,-1]
#dx8 = [1,1,0,-1,-1,-1,0,1]
#dy8 = [0,1,1,1,0,-1,-1,-1]


def main():
    N = int(input())
    A = list(map(int,input().split()))

    ans = (pow(2,N-1,MOD) - 1) * (A[0] - A[-1])
    print(ans%MOD)

if __name__ == '__main__':
    main()