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//#pragma optimization_level 3

//#pragma comment(linker, "/stack:200000000")
//#pragma GCC optimize("Ofast")
//#pragma GCC optimize("unroll-loops")
//#pragma GCC target("sse,sse2,sse3,ssse3,sse4,popcnt,abm,mmx,avx,tune=native")

#include <iostream>
#include <algorithm>
#include <vector>
#include <set>
#include <map>
#include <unordered_map>
#include <unordered_set>
#include <bitset>
#include <chrono>
#include <ctime>
#include <queue>
#include <math.h>
#include <deque>
#include <stack>
#include <iomanip>
#include <assert.h>
#include <stdio.h>
#include <cstring>
#include <random>

using namespace std;

#define int long long
#define ld long double
#define ull unsigned long long
#define endl '\n'
#define try tr
#define pii pair<int, int>
#define ti tuple <int, int, int>
#define vi vector <int>
#define vpi vector <pii>
#define umap unordered_map
#define uset unordered_set
#define left left11
#define right right11
#define all(c) (c).begin(), (c).end()
#define pb push_back
#define sqr(a) ((a) * (a))
#define fast ios_base::sync_with_stdio(0);cin.tie(0);cout.tie(0);

#define fs first
#define sc second

ld TL = 1.0;
bool is_tl = 0;
int CALLS = 0;

inline bool IS() {
    if (++CALLS == 1000) {
        CALLS = 0;
        is_tl |= clock() > (TL - 0.1) * CLOCKS_PER_SEC;
    }
    return is_tl;
}

template<typename T1, typename T2>
inline void amin(T1 &a, T2 b) { if (a > b) a = b; }

template<typename T1, typename T2>
inline void amax(T1 &a, T2 b) { if (a < b) a = b; }

template<typename T1, typename T2>
ostream &operator<<(ostream &os, pair<T1, T2> &p) {
    os << p.first << ' ' << p.second << endl;
    return os;
}

template<typename T1, typename T2>
istream &operator>>(istream &is, pair<T1, T2> &p) {
    is >> p.first >> p.second;
    return is;
}

template<typename T>
ostream &operator<<(ostream &os, vector<T> &v) {
    for (auto &u : v) os << u << ' ';
    os << endl;
    return os;
}

mt19937 rnd(chrono::steady_clock::now().time_since_epoch().count());
const int N = 1e6 + 7, NS = 2e3 + 7, lg = 19, sq = 550, inf = 1e9 + 7, SM = 51;
const ld eps = 1e-9;

void solve() {
    int n, k, sum = 0, cur = 0, ans = 0;
    cin >> n >> k;
    vi a(n);
    for (int i = 0; i < n; i++) {
        cin >> a[i];
        if(a[i] > 0)
            sum += a[i];
    }
    for (int i = 0; i < k; i++) {
        if(a[i] > 0)
          sum -= a[i];
        cur += a[i];
    }
    amax(ans, max(0ll, cur) + sum);
    for (int i = k; i < n; i++) {
        if(a[i] > 0)
            sum -= a[i];
        cur += a[i];
        if(a[i - k] > 0)
            sum += a[i - k];
        cur -= a[i - k];
        amax(ans, max(0ll, cur) + sum);
    }
    cout << ans;
}

signed main() {
    fast
    solve();
}

Measured memory_bytes: 3972