#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);
    }

    int li, ri;
    li = ri = k;
    ll ld = x.at(k) - a.at(k);
    ll rd = x.at(k) + a.at(k);

    bool update = true;
    while (update) {
        update = false;

        if (0 <= li - 1 && ld <= x.at(li - 1)) {
            li--;
            ld = min(ld, x.at(li) - a.at(li));
            rd = max(rd, x.at(li) + a.at(li));
            update = true;
        }

        if (ri + 1 < n && x.at(ri + 1) <= rd) {
            ri++;
            ld = min(ld, x.at(ri) - a.at(ri));
            rd = max(rd, x.at(ri) + a.at(ri));
            update = true;
        }
    }
    cout << ri - li + 1 << endl;
}