class Program
{
    static void Main()
    {
        int[] nm = Console.ReadLine().Split().Select(_ => int.Parse(_)).ToArray();
        int N = nm[0];
        int M = nm[1];

        int[] A = Console.ReadLine().Split().Select(_ => int.Parse(_)).ToArray();
        int[] B = Console.ReadLine().Split().Select(_ => int.Parse(_)).ToArray();

        int[] C = new int[N];
        for (int i = 0; i < N; i++)
            C[i] = Math.Max(A[i] - B[i], 0);

        long[] sums = new long[N + 1];
        for (int i = 0; i < N; i++)
            sums[i + 1] = sums[i] + C[i];

        long ans = 0;
        for (int i = 0; i + M - 1 < N; i++)
            ans = Math.Max(ans, sums[i + M] - sums[i]);

        Console.WriteLine(ans);
    }
}