#include <bits/stdc++.h>
using namespace std;

#define rep(i,n) for(int i = 0; i < (int)n; i++)
#define FOR(n) for(int i = 0; i < (int)n; i++)
#define repi(i,a,b) for(int i = (int)a; i < (int)b; i++)
#define pb push_back
#define m0(x) memset(x,0,sizeof(x))
#define fill(x,y) memset(x,y,sizeof(x))
#define bg begin()
#define ed end()
#define all(x) x.bg,x.ed
//#define mp make_pair
#define vi vector<int>
#define vvi vector<vi>
#define vll vector<ll>
#define vvll vector<vll>
#define vs vector<string>
#define vvs vector<vs>
#define vc vector<char>
#define vvc vector<vc>
#define pii pair<int,int>
#define pllll pair<ll,ll>
#define vpii vector<pair<int,int>>
#define vpllll vector<pair<ll,ll>>
#define vpis vector<pair<int,string>>
#define vplls vector<pair<ll, string>>
#define vpsi vector<pair<string, int>>
#define vpsll vector<pair<string, ll>>

template<typename T>
void chmax(T &a, const T &b) {a = (a > b? a : b);}
template<typename T>
void chmin(T &a, const T &b) {a = (a < b? a : b);}

using ll = long long;
using ld = long double;
using ull = unsigned long long;

const ll INF = numeric_limits<long long>::max() / 2;
const ld pi = 3.1415926535897932384626433832795028;
const ll mod = 1e9 + 7;
int dx[] = {-1, 0, 1, 0, -1, -1, 1, 1};
int dy[] = {0, -1, 0, 1, -1, 1, -1, 1};

#define int long long
template<typename T>
struct Abstruct_SegmentTree {
    function<T(T, T)> f;
    const T E;

    vector<T> dat;
    int n;

    Abstruct_SegmentTree(int n_, T e, function<T(T, T)> F) : E(e), dat(4*n_, e) {
        f = F;
        int x = 1;
        while(x < n_) x *= 2;
        n = x;
    }

    void update(int i, T x) {
        i += n - 1;
        dat[i] = x;

        while(i > 0) {
            i = (i - 1) / 2;
            dat[i] = f(dat[i * 2 + 1], dat[i * 2 + 2]);
        }

        return;
    }

    T query(int a, int b) {
        return query_sub(a, b, 0, 0, n);
    }

    T query_sub(int a, int b, int k, int l, int r) {
        if(b <= l || r <= a) {
            return E;
        }else if(a <= l && r <= b) {
            return dat[k];
        }else {
            T vl = query_sub(a, b, k * 2 + 1, l, (l + r) / 2);
            T vr = query_sub(a, b, k * 2 + 2, (l + r) / 2, r);
            return f(vl, vr);
        }
    }

    inline T operator[](const int i) {
        return query(i, i+1);
    }

    void print() {
        cout << "{";
        for(int i = 0; i < n; i++) {
            cout << (*this)[i];
            if(i != n-1) cout << ", ";
        }
        cout << "}";
        cout << "\n";
    }
};

auto f = [](pii p, pii q) -> pii {
    if(p.first != q.first) {
        if(p.first > q.first) return p;
        return q;
    }
    if(p.second > q.second) return p;
    return q;
};


void solve() {
    int n, k;
    cin >> n >> k;
    vi a(n);
    FOR(n) cin >> a[i];
    //最初に奇数が乗ったらダメ
    vector<bool> used(n, false);
    int cnt = 0;
    int now = 0;
    int ans = 0;
    Abstruct_SegmentTree<pii> seg(n, {-1, -1}, f);
    FOR(n) seg.update(i, {a[i], i});

    for(int i = 1; i < n-k+1; i++) {
        if(i&1) {
            while(cnt < k-1) {
                pii p = seg.query(i, n);
                now += p.first;
                used[p.second] = true;
                seg.update(p.second, {-1, -1});
                cnt++;
            }

            if(used[i]) {
                pii p = seg.query(i, n);
                now += p.first;
                used[p.second] = true;
                seg.update(p.second, {-1, -1});
                cnt++;
                chmax(ans, now);
            }else {
                chmax(ans, now + a[i]);
            }

            if(used[i]) cnt--, now -= a[i];
        }else {
            if(used[i]) cnt--, now -= a[i];
        }
    }

    cout << ans << endl;
}

signed main() {
    cin.tie(nullptr);
    ios::sync_with_stdio(false);
    solve();
    return 0;
}