n = int(input())
a = list(map(int, input().split()))
s = [0]*n
for i in range(1,n):
    s[i] = s[i-1] + pow(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)