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 ans: usize = 1;
  let mut wave_range = x[k] + a[k];
  // 右側のカエル
  for i in k+1..n {
    if wave_range >= x[i] {
      wave_range = max(wave_range, x[i] + a[i]);
      ans += 1;
    }
  }

  let mut wave_range = x[k] - a[k];
  // 左側のカエル
  for i in (0..k).rev() {
    if wave_range <= x[i] {
      wave_range = min(wave_range, x[i] - a[i]);
      ans += 1;
    }
  }

  println!("{}", ans);
}