import java.util.*;
import java.io.*;

public class Main {
	public static void main (String[] args) throws Exception {
		BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
		String[] first = br.readLine().split(" ", 2);
		int n = Integer.parseInt(first[0]);
		int k = Integer.parseInt(first[1]) - 1;
		String[] second = br.readLine().split(" ", n);
		String[] third = br.readLine().split(" ", n);
		Frog[] frogs = new Frog[n];
		for (int i = 0; i < n; i++) {
		    frogs[i] = new Frog(Long.parseLong(second[i]), Long.parseLong(third[i]));
		}
		int left = k;
		int right = k;
		long min = frogs[k].position - frogs[k].strength;
		long max = frogs[k].position + frogs[k].strength;
		boolean flag = true;
		while (flag) {
		    flag = false;
		    while (left > 0 && frogs[left - 1].position >= min) {
		        min = Math.min(min, frogs[left - 1].position - frogs[left - 1].strength);
		        max = Math.max(max, frogs[left - 1].position + frogs[left - 1].strength);
		        left--;
		        flag = true;
		    }
		    while (right < n - 1 && frogs[right + 1].position <= max) {
		        min = Math.min(min, frogs[right + 1].position - frogs[right + 1].strength);
		        max = Math.max(max, frogs[right + 1].position + frogs[right + 1].strength);
		        right++;
		        flag = true;
		    }
		}
		System.out.println(right - left + 1);
   }
   
   static class Frog {
       long position;
       long strength;
       
       public Frog(long position, long strength) {
           this.position = position;
           this.strength = strength;
       }
   }
}