n = int(input())
a = list(map(int, input().split()))
s = [0]*n
for i in range(1,n):
    s[i] = s[i-1] + 2**(i-1)
# print(s)
res = 0
mod = 998244353
for i in range(n-1):
    res += (a[i]-a[-1+i])*s[-1+i]
    res %= mod
print(res)


# tot = sum(a)
# mod = 998244353
# res = 0
# if n == 2:
#     res += (a[0]-a[-1])
#     res %= mod
#     print(res)
#     exit(0)
# cur = n
# for aa in a:
#     cur -= 1
#     res += (aa*cur)-(tot-aa)
#     tot -= aa
#     res %= mod
# res += (a[0]-a[-1])
# res %= mod
# print(res)