use std::io::*;
fn main() {
    let mut s: String = String::new();
    std::io::stdin().read_to_string(&mut s).ok();
    let mut itr = s.trim().split_whitespace();
    let n: usize = itr.next().unwrap().parse().unwrap();
    let k: usize = itr.next().unwrap().parse::<usize>().unwrap() - 1;
    let x: Vec<i64> = (0..n)
        .map(|_| itr.next().unwrap().parse().unwrap())
        .collect();
    let a: Vec<i64> = (0..n)
        .map(|_| itr.next().unwrap().parse().unwrap())
        .collect();


    let mut left = k;
    let mut lv = x[k] - a[k];
    let mut right = k;
    let mut rv = x[k] + a[k];
    while left > 0 {
        if x[left - 1] >= lv {
            lv = std::cmp::min(lv, x[left - 1] - a[left - 1]);
            left -= 1;
        } else {
            break;
        }
    }
    while right < n - 1 {
        if x[right + 1] <= rv {
            rv = std::cmp::max(rv, x[right + 1] + a[right + 1]);
            right += 1;
        } else {
            break;
        }
    }

    println!("{}", right - left + 1);
}