#include <bits/stdc++.h>
using namespace std;
#define rep(i, n) for (int i = 0; i < (n); ++i)
using ll = long long;
using ull = unsigned long long;

int main() {
  cin.tie(nullptr)->sync_with_stdio(false);
  int n, k;
  cin >> n >> k;
  --k;
  vector<ll> x(n), a(n);
  rep(i, n) cin >> x[i];
  rep(i, n) cin >> a[i];
  pair<ll, ll> rng = { x[k] - a[k], x[k] + a[k] };
  pair<int, int> idx = { k, k };
  {
    bool upd = true;
    while (upd) {
      upd = false;
      for (int i = idx.first - 1; i >= 0; --i) {
        if (rng.first > x[i]) break;
        rng.first = min(rng.first, x[i] - a[i]);
        rng.second = max(rng.second, x[i] + a[i]);
        idx.first = i;
        upd = true;
      }
      for (int i = idx.second + 1; i < n; ++i) {
        if (rng.second < x[i]) break;
        rng.first = min(rng.first, x[i] - a[i]);
        rng.second = max(rng.second, x[i] + a[i]);
        idx.second = i;
        upd = true;
      }
    }
  }
  cout << idx.second - idx.first + 1 << '\n';
  return 0;
}