use itertools::Itertools;
use proconio::{fastout, input};

#[fastout]
fn main() {
    input! {
        n: usize,
        m: usize,
        a: [i64; n],
        b: [i64; n],
    }
    let d = (0..n).map(|i| (a[i] - b[i]).max(0)).collect_vec();
    let mut sum = d[0..m].iter().sum::<i64>();
    let mut ans = sum;
    for i in m..n {
        sum += -d[i - m] + d[i];
        ans = ans.max(sum);
    }

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