#include <iostream>
#include <vector>
#include <algorithm>

using namespace std;

int main() {
	int n, k;
	cin >> n >> k;
	vector<long long> x(n), a(n);
	for (int i = 0; i < n; ++i) {
		cin >> x[i];
	}
	for (int i = 0; i < n; ++i) {
		cin >> a[i];
	}
	long long frontX = x[k - 1] - a[k - 1];
	long long backX = x[k - 1] + a[k - 1];
	int frontIndex = k - 1 - 1;
	int backIndex = k - 1 + 1;
	for (;;) {
		bool newlySung = false;
		if (frontIndex >= 0 && frontX <= x[frontIndex]) {
			frontX = min(frontX, x[frontIndex] - a[frontIndex]);
			backX = max(backX, x[frontIndex] + a[frontIndex]);
			--frontIndex;
			newlySung = true;
		}
		if (backIndex < n && x[backIndex] <= backX) {
			backX = max(backX, x[backIndex] + a[backIndex]);
			frontX = min(frontX, x[backIndex] - a[backIndex]);
			++backIndex;
			newlySung = true;
		}
		if (!newlySung) {
			break;
		}
	}
	cout << (backIndex - frontIndex - 2 + 1) << endl;
	return 0;
}