#[allow(unused_macros)]
macro_rules! debug {
($($e:expr), *) => {println!(concat!($(stringify!($e), " = {:?}\n"), *), $($e), *)}
}
fn main() {
let (n, k) = get::tuple::<usize,usize>();
let xs = get::list::<isize>();
let mut mi = 0;
let mut mj = k - 1;
let mut acc = xs[0..k].iter().sum::<isize>();
let mut max = std::cmp::max(0, acc);
for a in 1 .. n {
acc = acc - xs[a-1] + xs[(a+k-1)%n];
if acc > max {
max = acc;
mi = a;
mj = a + k - 1;
}
}
let sum_rest = {
if mj < n {
let init = xs[..mi].iter().filter(|&&x|x.is_positive()).sum::<isize>();
let tail = xs[mj+1..].iter().filter(|&&x|x.is_positive()).sum::<isize>();
init + tail
} else {
xs[mj%n+1..mi].iter().filter(|&&x|x.is_positive()).sum::<isize>()
}
};
println!("{}", max + sum_rest)
}
#[allow(dead_code)]
mod get {
use std::io::*;
use std::str::*;
pub fn val<T: FromStr>() -> T {
let mut buf = String::new();
let s = stdin();
s.lock().read_line(&mut buf).ok();
buf.trim_right().parse::<T>().ok().unwrap()
}
pub fn vals<T: FromStr>(n: usize) -> Vec<T> {
let mut vec: Vec<T> = vec![];
for _ in 0 .. n {
vec.push(val());
}
vec
}
pub fn tuple<T1: FromStr, T2: FromStr>() -> (T1, T2) {
let mut buf = String::new();
let s = stdin();
s.lock().read_line(&mut buf).ok();
let mut it = buf.trim_right().split_whitespace();
let x = it.next().unwrap().parse::<T1>().ok().unwrap();
let y = it.next().unwrap().parse::<T2>().ok().unwrap();
(x, y)
}
pub fn tuples<T1: FromStr, T2: FromStr>(n: usize) -> Vec<(T1, T2)> {
let mut vec: Vec<(T1, T2)> = vec![];
for _ in 0 .. n {
vec.push(tuple());
}
vec
}
pub fn tuple3<T1: FromStr, T2: FromStr, T3: FromStr>() -> (T1, T2, T3) {
let mut buf = String::new();
let s = stdin();
s.lock().read_line(&mut buf).ok();
let mut it = buf.trim_right().split_whitespace();
let x = it.next().unwrap().parse::<T1>().ok().unwrap();
let y = it.next().unwrap().parse::<T2>().ok().unwrap();
let z = it.next().unwrap().parse::<T3>().ok().unwrap();
(x, y, z)
}
pub fn tuple3s<T1: FromStr, T2: FromStr, T3: FromStr>(n: usize) -> Vec<(T1, T2, T3)> {
let mut vec: Vec<(T1, T2, T3)> = vec![];
for _ in 0 .. n {
vec.push(tuple3());
}
vec
}
pub fn list<T: FromStr>() -> Vec<T> {
let mut buf = String::new();
let s = stdin();
s.lock().read_line(&mut buf).ok();
buf.trim_right().split_whitespace().map(|t| t.parse::<T>().ok().unwrap()).collect()
}
pub fn lists<T: FromStr>(h: usize) -> Vec<Vec<T>> {
let mut mat: Vec<Vec<T>> = vec![];
for _ in 0 .. h {
mat.push(list());
}
mat
}
pub fn chars() -> Vec<char> {
let mut buf = String::new();
let s = stdin();
s.lock().read_line(&mut buf).ok();
buf.trim_right().chars().collect()
}
}