#include <iostream>
#include <vector>

using lint = long long;

void solve() {
    int n, k;
    std::cin >> n >> k;
    --k;

    std::vector<lint> xs(n), ys(n);
    for (auto& x : xs) std::cin >> x;
    for (auto& y : ys) std::cin >> y;

    int li = k, ri = k;
    lint l = xs[k] - ys[k], r = xs[k] + ys[k];

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

        while (li - 1 >= 0 && xs[li - 1] >= l) {
            update = true;
            --li;

            l = std::min(l, xs[li] - ys[li]);
            r = std::max(r, xs[li] + ys[li]);
        }

        while (ri + 1 < n && xs[ri + 1] <= r) {
            update = true;
            ++ri;

            l = std::min(l, xs[ri] - ys[ri]);
            r = std::max(r, xs[ri] + ys[ri]);
        }
    }

    std::cout << ri - li + 1 << std::endl;
}

int main() {
    std::cin.tie(nullptr);
    std::ios::sync_with_stdio(false);

    solve();

    return 0;
}