#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];
  int l, r;
  {
    ll cur = x[k] - a[k];
    for (int i = k; i >= 0; --i) {
      if (cur > x[i]) break;
      cur = min(cur, x[i] - a[i]);
      l = i;
    }
  }
  {
    ll cur = x[k] + a[k];
    for (int i = k; i < n; ++i) {
      if (cur < x[i]) break;
      cur = max(cur, x[i] + a[i]);
      r = i;
    }
  }
  cout << r - l + 1 << '\n';
  return 0;
}