using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;

namespace FreeWorks
{
    class Program
    {
        static void Main(string[] args)
        {
            string[] line = Console.ReadLine().Split(' ');
            int n = int.Parse(line[0]);
            int k = int.Parse(line[1]);
            long[] X = Console.ReadLine().Split(' ').Select(x => long.Parse(x)).ToArray();
            long[] A = Console.ReadLine().Split(' ').Select(x => long.Parse(x)).ToArray();

            bool[] check = new bool[n];


            Queue<int> q = new Queue<int>();
            q.Enqueue(k - 1);
            int cnt = 0;
            int max_i = k - 1;
            int min_i = k - 1;
            while (q.Count > 0)
            {
                int i = q.Dequeue();
                if (check[i]) continue;
                check[i] = true;
                cnt++;
                long rightRange = X[i] + A[i];
                long leftRange = X[i] - A[i];

                for (int x = max_i + 1; x < n && X[x] <= rightRange; x++)
                {
                    q.Enqueue(x);
                    max_i = Math.Max(max_i, x);
                }

                for (int x = min_i - 1; x >= 0 && leftRange <= X[x]; x--)
                {
                    q.Enqueue(x);
                    min_i = Math.Min(min_i, x);
                }

            }

            Console.WriteLine(cnt);
        }
    }
}