#include<stdio.h>
int main()
{
	int n, k;
	scanf("%d %d", &n, &k);
	k--;
	int i;
	long long int x[100005], a[100005];
	for (i = 0; i < n; i++)
		scanf("%lld", &x[i]);
	for (i = 0; i < n; i++)
		scanf("%lld", &a[i]);
	int ans = 1;
	for (i = k; i > 0; i--)
	{
		if (x[i] - x[i - 1] <= a[i])
			ans++;
		else
			break;
	}
	for (i = k; i < n - 1; i++)
	{
		if (x[i + 1] - x[i] <= a[i])
			ans++;
		else
			break;
	}
	printf("%d\n", ans);
	return 0;
}