using System;

public class Program

{

    public static void Main()

    {

        int n = Convert.ToInt32(Console.ReadLine());

        int length = Convert.ToInt32(Console.ReadLine());

        int[] pos = new int[n];

        int[] dir = new int[n];

        int[] dist = new int[n];

        string[] str1 = Console.ReadLine().Split(' ');

        string[] str2 = Console.ReadLine().Split(' ');

        int max = 0;

        for (int i = 0; i < n; i++)

        {

            pos[i] = Convert.ToInt32(str1[i]);

            dir[i] = Convert.ToInt32(str2[i]);

            if (dir[i] == 1)

                dist[i] = length - pos[i];

            else

                dist[i] = pos[i];

            if (dist[i] > max)

                max = dist[i];

        }

        Console.WriteLine(max);

    }

}