X = int(input())
Y = list(map(int, input().split()))

def s(y):
    return y * (y + 1) // 2

ans = 0
add = 0
toy = 1
mod = 998244353
for y in Y:
    ans += y * add + s(y) * toy + (y - 1) * y * (y + 1) // 6
    ans %= mod
    add += s(y)
    toy += y
print(ans)