import std.algorithm;
import std.array;
import std.ascii;
import std.bigint;
import std.complex;
import std.container;
import std.conv;
import std.functional;
import std.math;
import std.range;
import std.stdio;
import std.string;
import std.typecons;

auto readInts() {
	return array(map!(to!int)(readln().strip().split()));
}
auto readInt() {
	return readInts()[0];
}
auto readLongs() {
	return array(map!(to!long)(readln().strip().split()));
}
auto readLong() {
	return readLongs()[0];
}

void readlnTo(T...)(ref T t) {
    auto s = readln().split();
    assert(s.length == t.length);
    foreach(ref ti; t) {
        ti = s[0].to!(typeof(ti));
        s = s[1..$];
    }
}

const real eps = 1e-10;

void main(){
    int N, K;
    readlnTo(N, K);
    auto a = readLongs();
    long ans = long.min;
    long[] t = [0];
    foreach(i; iota(N)) {
        t ~= t.back + max(a[i], 0);
    }
    long S;
    foreach(i; iota(K)){ 
        S += a[i];
    }
    foreach(i; iota(N-K+1)) {
        ans = max(ans, t[i] + max(S, 0) + t.back - t[i+K]);
        if(i < N-K) {
            S = S - a[i] + a[i+K];
        }
    }
    writeln(ans);
}

