#include <bits/stdc++.h>
using namespace std;
#include <atcoder/all>
using namespace atcoder;
using ll = long long;
using vi = vector<int>;
using vvi = vector<vector<int>>;
using pii = pair<int, int>;
#define rep(i, n) for (int i = 0; i < (int)(n); ++i)
#define repr(i, n) for (int i = (int)(n - 1); i >= 0; --i)

int main() {
    int n, K;
    cin >> n >> K;
    vi a(n);
    rep(i, n) cin >> a[i];
    ll ret = 0;
    ll s = 0;
    priority_queue<ll, vector<ll>, greater<ll>> pq;
    repr(i, n) {
        if (pq.size() > K - 1) {
            s -= pq.top();
            pq.pop();
        }
        s += a[i];
        pq.emplace(a[i]);
        if (i & 1) ret = max(ret, s);
    }
    cout << ret << endl;
    return 0;
}