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

using namespace std;

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