#[macro_export]
macro_rules! setup {
    { mut $input:ident: SplitWhitespace $(,)? } => {
        use std::io::Read;
        let mut buf = String::new();
        std::io::stdin().read_to_string(&mut buf).ok();
        let mut $input = buf.split_whitespace();
    };
}

#[macro_export]
macro_rules! parse_next {
    ($str_iter:expr) => {
        $str_iter.next().unwrap().parse().ok().unwrap()
    };
}

#[allow(unused_imports)]
use std::collections::{HashMap, HashSet, VecDeque};

fn main() {
    setup! { mut input: SplitWhitespace };

    let n: usize = parse_next!(input);
    let k: usize = parse_next!(input);
    let x: Vec<i64> = (0..n).map(|_| parse_next!(input)).collect();
    let a: Vec<i64> = (0..n).map(|_| parse_next!(input)).collect();

    let ans = (|| {
        let mut queue = VecDeque::new();
        let mut visited = HashSet::new();
        {
            let root = k - 1;
            queue.push_back(root);
            visited.insert(root);
        }
        while !queue.is_empty() {
            let i = queue.pop_front().unwrap();
            let children = x
                .iter()
                .enumerate()
                .filter(|(_, x_j)| {
                    if (x[i] - a[i] <= **x_j) && (**x_j <= x[i] + a[i]) {
                        return true;
                    }
                    false
                })
                .map(|(j, _)| j)
                .collect::<Vec<_>>();
            for j in children.into_iter() {
                if visited.contains(&j) {
                    continue;
                }
                queue.push_back(j);
                visited.insert(j);
            }
        }
        visited.len()
    })();

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