#include <bits/stdc++.h>
using namespace std;

using ll = long long;

int main() {
    int n, k;
    cin >> n >> k;
    k--;
    vector<ll> x(n), a(n);
    for (int i = 0; i < n; i++) {
        cin >> x.at(i);
    }
    for (int i = 0; i < n; i++) {
        cin >> a.at(i);
    }

    ll d = a.at(k);
    int cnt = 1;
    for (int i = k + 1; i < n; i++) {
        if (x.at(i) - x.at(i - 1) <= d) {
            cnt++;
            d = max(d - (x.at(i) - x.at(i - 1)), a.at(i));
        }
        else break;
    }

    d = a.at(k);
    for (int i = k - 1; i >= 0; i--) {
        if (x.at(i + 1) - x.at(i) <= d) {
            cnt++;
            d = max(d - (x.at(i + 1) - x.at(i)), a.at(i));
        }
        else break;
    }

    cout << cnt << endl;
}