#define _USE_MATH_DEFINES
#include <bits/stdc++.h>
using namespace std;
signed main() {
  ios::sync_with_stdio(false); cin.tie(0);
  int n, k;
  cin >> n >> k;
  k--;
  vector<long long> x(n), a(n);
  for (int i = 0; i < n; i++) {
    cin >> x[i];
  }
  for (int i = 0; i < n; i++) {
    cin >> a[i];
  }
  int ans = 1;
  int l = k - 1, r = k + 1;
  long long left = x[k] - a[k], right = x[k] + a[k];
  while (true) {
    bool update = false;
    while (l >= 0 && left <= x[l]) {
      update = true;
      ans++;
      left = min(left, x[l] - a[l]);
      right = max(right, x[l] + a[l]);
      l--;
    }
    while (r < n && right >= x[r]) {
      update = true;
      ans++;
      right = max(right, x[r] + a[r]);
      left = min(left, x[r] - a[r]);
      r++;
    }
    if (!update) break;
  }
  cout << ans << endl;
  return 0;
}