use proconio::input;
fn main() {
    input! {
        n: usize,
        m: usize,
        a: [u64; n],
        b: [u64; n],
    }

    let c = a.iter().zip(&b).map(|(&ai, &bi)| ai.saturating_sub(bi));
    let mut acc = vec![0; n + 1];
    for (i, ci) in c.enumerate() {
        acc[i + 1] = acc[i] + ci;
    }

    let mut ans = 0;
    for (&l, &r) in acc.iter().zip(&acc[m..]) {
        ans = ans.max(r - l);
    }
    println!("{ans}");
}