use std::collections::VecDeque;

fn lower_bound(val: isize, target: &Vec<isize>) -> usize {
    let mut lower = 0usize;
    let mut upper = target.len();
    while upper > lower {
        let middle = (upper + lower) / 2;
        if val <= target[middle] {
            upper = middle;
        } else {
            lower = middle+1;
        }
    }
    upper
}

fn upper_bound(val: isize, target: &Vec<isize>) -> usize {
    let mut lower = 0usize;
    let mut upper = target.len();
    while upper > lower {
        let middle = (upper + lower) / 2;
        if val < target[middle] {
            upper = middle;
        } else {
            lower = middle+1;
        }
    }
    upper
}

fn main() {
    let mut nk = String::new();
    std::io::stdin().read_line(&mut nk).ok();
    let nk: Vec<usize> = nk.trim().split_whitespace().map(|s| s.parse().unwrap()).collect();
    let n = nk[0];
    let k = nk[1]-1;
    let mut x = String::new();
    std::io::stdin().read_line(&mut x).ok();
    let x: Vec<isize> = x.trim().split_whitespace().map(|s| s.parse().unwrap()).collect();
    let mut a = String::new();
    std::io::stdin().read_line(&mut a).ok();
    let a: Vec<isize> = a.trim().split_whitespace().map(|s| s.parse().unwrap()).collect();

    let mut checked = vec![false; n];
    let mut deque = VecDeque::new();
    deque.push_back(k);
    checked[k] = true;
    while let Some(idx) = deque.pop_front() {
        let left = x[idx] - a[idx];
        let right = x[idx] + a[idx];
        let lidx = lower_bound(left, &x);
        let ridx = upper_bound(right, &x);
        for i in lidx.. {
            if checked[i] { break; }
            deque.push_back(i);
            checked[i] = true;
        }
        for i in (idx..ridx).rev() {
            if checked[i] { break; }
            deque.push_back(i);
            checked[i] = true;
        }
    }
    println!("{}", checked.iter().filter(|&&v| v).count());
}