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[] xArr = new long[n + 2];
		for (int i = 1; i <= n; i++) {
		    xArr[i] = sc.nextLong();
		}
		xArr[0] = Long.MIN_VALUE;
		xArr[n + 1] = Long.MAX_VALUE;
		long[] aArr = new long[n + 1];
		for (int i = 1; i <= n; i++) {
		    aArr[i] = sc.nextLong();
		}
		int min = Integer.MAX_VALUE;
		int target = k;
		while (min != target) {
		    min = target;
		    int left = 0;
		    int right = target;
		    while (right - left > 1) {
		        int m = (left + right) / 2;
		        if (xArr[target] - xArr[m] <= aArr[target]) {
		            right = m;
		        } else {
		            left = m;
		        }
		    }
		    target = right;
		}
		int max = Integer.MIN_VALUE;
		target = k;
		while (max != target) {
		    max = target;
		    int left = target;
		    int right = n;
		    while (right - left > 1) {
		        int m = (left + right) / 2;
		        if (xArr[m] - xArr[target] <= aArr[target]) {
		            left = m;
		        } else {
		            right = m;
		        }
		    }
		    target = left;
		}
		System.out.println(max - min + 1);
	}
}