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];
    loop {
        let mut updated = false;
        let mut tmpl = lv;
        let mut tmpr = rv;

        while left > 0 && lv <= x[left - 1] {
            updated = true;
            left -= 1;
            tmpl = std::cmp::min(tmpl, x[left] - a[left]);
            tmpr = std::cmp::max(tmpr, x[left] + a[left]);
        }
        while right < n - 1 && rv >= x[right + 1] {
            updated = true;
            right += 1;
            tmpl = std::cmp::min(tmpl, x[right] - a[right]);
            tmpr = std::cmp::max(tmpr, x[right] + a[right]);
        }
        lv = tmpl;
        rv = tmpr;
        if !updated {
            break;
        }
    }

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