using System.Diagnostics;
class Program
{
    static string ReadLine() => Console.ReadLine().Trim();
    static int ReadInt() => int.Parse(ReadLine());
    static long ReadLong() => long.Parse(ReadLine());
    static int[] ReadIntArray() { string str = ReadLine(); return str != "" ? str.Split().Select(_ => int.Parse(_)).ToArray() : new int[0]; }
    static long[] ReadLongArray() { string str = ReadLine(); return str != "" ? str.Split().Select(_ => long.Parse(_)).ToArray() : new long[0]; }
    static (int, int) ReadInt2() { int[] vs = ReadIntArray(); return (vs[0], vs[1]); }
    static (int, int, int) ReadInt3() { int[] vs = ReadIntArray(); return (vs[0], vs[1], vs[2]); }
    static (int, int, int, int) ReadInt4() { int[] vs = ReadIntArray(); return (vs[0], vs[1], vs[2], vs[3]); }
    static (int, int, int, int, int) ReadInt5() { int[] vs = ReadIntArray(); return (vs[0], vs[1], vs[2], vs[3], vs[4]); }
    static (long, long) ReadLong2() { long[] vs = ReadLongArray(); return (vs[0], vs[1]); }
    static (long, long, long) ReadLong3() { long[] vs = ReadLongArray(); return (vs[0], vs[1], vs[2]); }

    static void Main()
    {
        SourceExpander.Expander.Expand();

        (int N, int M) = ReadInt2();
        int[] A = ReadIntArray();
        int[] B = ReadIntArray();

        int[] C = new int[N];
        int[] plus = new int[N];
        for (int i = 0; i < N; i++)
        {
            C[i] = A[i] - B[i];
            if(C[i] > 0)
                plus[i] = C[i];
        }

        long[] plus_sum = new long[N + 1];
        for (int i = 0; i < N; i++)
        {
            plus_sum[i + 1] = plus_sum[i] + plus[i];
        }

        long ans = 0;
        for (int i = 0; i + M - 1 < N; i++)
        {
            ans = Math.Max(ans, plus_sum[i + M] - plus_sum[i]);
        }
        Console.WriteLine(ans);
    }
}
#region Expanded by https://github.com/kzrnm/SourceExpander
namespace SourceExpander{public class Expander{[Conditional("EXP")]public static void Expand(string inputFilePath=null,string outputFilePath=null,bool ignoreAnyError=true){}public static string ExpandString(string inputFilePath=null,bool ignoreAnyError=true){return "";}}}
#endregion Expanded by https://github.com/kzrnm/SourceExpander