using System;
using static System.Console;
using System.Linq;
using System.Collections.Generic;

class Program
{
    static int NN => int.Parse(ReadLine());
    static long[] NList => ReadLine().Split().Select(long.Parse).ToArray();
    public static void Main()
    {
        Solve();
    }
    static void Solve()
    {
        var c = NList;
        var (n, k) = ((int)c[0], (int)c[1] - 1);
        var x = NList;
        var a = NList;
        var left = k;
        var right = k;
        var q = new Queue<int>();
        q.Enqueue(k);
        var ans = 1;
        while (q.Count > 0)
        {
            var cur = q.Dequeue();
            var nl = LowerBound(x[cur] - a[cur], x);
            var nr = UpperBound(x[cur] + a[cur], x) - 1;
            while (nl < left)
            {
                ++ans;
                --left;
                q.Enqueue(left);
            }
            while (right < nr)
            {
                ++ans;
                ++right;
                if (right < n) q.Enqueue(right);
            }
        }
        WriteLine(ans);
    }
    static int LowerBound<T>(T min, IList<T> list) where T: IComparable<T>
    {
        var ng = -1;
        var ok = list.Count;
        while (ok - ng > 1)
        {
            var mid = (ng + ok) / 2;
            if (list[mid].CompareTo(min) < 0) ng = mid;
            else ok = mid;
        }
        return ok;
    }
    static int UpperBound<T>(T min, IList<T> list) where T: IComparable<T>
    {
        var ng = -1;
        var ok = list.Count;
        while (ok - ng > 1)
        {
            var mid = (ng + ok) / 2;
            if (list[mid].CompareTo(min) <= 0) ng = mid;
            else ok = mid;
        }
        return ok;
    }
}