#include <bits/stdc++.h>
using namespace std;
using lint = long long;
template<class T = int> using V = vector<T>;
template<class T = int> using VV = V< V<T> >;

int main() {
  cin.tie(nullptr); ios::sync_with_stdio(false);
  int n, k; cin >> n >> k, --k;
  V<lint> x(n); for (auto&& e : x) cin >> e;
  V<lint> a(n); for (auto&& e : a) cin >> e;
  int res = -1;
  lint t = x[k] + a[k];
  for (int i = k; i < n; ++i) {
    if (t < x[i]) break;
    ++res;
    t = max(t, x[i] + a[i]);
  }
  t = x[k] - a[k];
  for (int i = k; i >= 0; --i) {
    if (x[i] < t) break;
    ++res;
    t = min(t, x[i] - a[i]);
  }
  cout << res << '\n';
}