use std::vec::Vec;
use std::cmp::min;
use std::cmp::max;


fn read<T: std::str::FromStr>() -> T {
    let mut s = String::new();
    std::io::stdin().read_line(&mut s).ok();
    s.trim().parse().ok().unwrap()
}

fn read_vec<T: std::str::FromStr>() -> Vec<T> {
    read::<String>().split_whitespace().map(|e| e.parse().ok().unwrap()).collect()
}

fn main() {
  let (n, k) = {
    let v: Vec<usize> = read_vec();
    (v[0], v[1] - 1)
  };
  let x: Vec<i64> = read_vec();
  let a: Vec<i64> = read_vec();

  let mut l = k;
  let mut r = k;
  let mut left = x[k] - a[k];
  let mut right = x[k] + a[k];
  let mut update = true;
  while update {
    update = false;
    // 左側のアップデート
    while l > 0 && left <= x[l-1] {
      update = true;
      left = min(x[l-1] - a[l-1], left);
      right = max(x[l-1] + a[l-1], right);
      l -= 1;
      //println!("{}", l);
    }

    while r + 1 < n && right >= x[r+1] {
      update = true;
      left = min(x[r+1] - a[r+1], left);
      right = max(x[r+1] + a[r+1], right);
      r += 1;
      //println!("{}", r);
    }
    //println!("l = {}, r = {}", l, r);
  }
  println!("{}", r - l +1);
}