import java.util.*;

public class Main {
    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        int n = sc.nextInt();
        int k = sc.nextInt() - 1;
        long[] idxes = new long[n];
        for (int i = 0; i < n; i++) {
            idxes[i] = sc.nextLong();
        }
        long[] values = new long[n];
        for (int i = 0; i < n; i++) {
            values[i] = sc.nextLong();
        }
        long left = idxes[k] - values[k];
        long right = idxes[k] + values[k];
        int plus = k;
        int minus = k;
        int plusOrg = -1;
        int minusOrg = -1;
        while (plus != plusOrg || minus != minusOrg) {
            plusOrg = plus;
            minusOrg = minus;
            while (plus < n - 1 && idxes[plus + 1] <= right) {
                plus++;
                right = Math.max(right, idxes[plus] + values[plus]);
                left = Math.min(left, idxes[plus] - values[plus]);
            }
            while(minus > 0 && idxes[minus - 1] >= left) {
                minus--;
                left = Math.min(left, idxes[minus] - values[minus]);
                right = Math.max(right, idxes[minus] + values[minus]);
            }
        }
        System.out.println(plus - minus + 1);
    }
}