#include <bits/stdc++.h>
using namespace std;
using namespace placeholders;
using ll = long long;

class sum_class{
	vector<ll> v;
public:
	sum_class(const vector<ll>& vv){
		v.resize(vv.size() + 1, 0);
		partial_sum(begin(vv), end(vv), begin(v) + 1); }
	ll operator()(const ll x, const ll y){
		return v[y+1] - v[x]; } };

int main(){
	ll n, k;
	cin >> n >> k;

	vector<ll> v(n);
	for(auto& x : v) cin >> x;

	vector<ll> pv(n);
	transform(begin(v), end(v), begin(pv), [](const ll x){ return max(x, 0); });

	sum_class sv(v), spv(pv);

	ll rez = accumulate(begin(v), end(v), 0);

	for(ll i = 0, j = k-1; j < n; ++i, ++j){
		rez = max(rez, spv(0, i-1) + max(sv(i, j), 0) + spv(j+1, n-1)); }
	
	cout << rez << endl;

	return 0; }
