#include <cassert>
#include <cmath>
#include <algorithm>
#include <iostream>
#include <iomanip>
#include <climits>
#include <map>
#include <queue>
#include <set>
#include <cstring>
#include <vector>

using namespace std;
typedef long long ll;


int main() {
  int N, K;
  cin >> N >> K;

  vector<ll> A(N);
  for (int i = 0; i < N; ++i) {
    cin >> A[i];
  }

  ll ans = 0;
  ll sum = 0;
  priority_queue <ll, vector<ll>, greater<ll>> pque;

  for (int i = N - 1; i >= 1; --i) {
    ll a = A[i];
    pque.push(a);
    sum += a;

    if (i % 2 == 1) {
      ans = max(ans, sum);
    }

    if (pque.size() >= K) {
      ll v = pque.top();
      sum -= v;
      pque.pop();
    }
  }

  cout << ans << endl;

  return 0;
}