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