# https://yukicoder.me/problems/no/3697

MOD = 998244353


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

    a = N // K
    p = ((a - 1) * pow(N - 1, MOD -2, MOD)) % MOD

    a_sum = 0
    b_sum = 0
    ab_sum = 0
    for i in range(N):
        a_sum += A[i]
        a_sum %= MOD
        b_sum += B[i]
        b_sum %= MOD
        ab_sum += (A[i] * B[i]) % MOD
        ab_sum %= MOD

    ans = (a_sum * b_sum) %MOD
    ans -= ab_sum
    ans %= MOD

    answer = (p * ans) % MOD
    print(answer)

        


                        



        

    


if __name__ == "__main__":
    main()