#include <bits/stdc++.h>
using namespace std;
int main(){
  int N, K;
  cin >> N >> K;
  vector<int> A(N);
  for (int i = 0; i < N; i++){
    cin >> A[i];
  }
  priority_queue<int, vector<int>, greater<int>> pq;
  long long ans = 0;
  long long sum = 0;
  for (int i = N - 1; i >= 0; i--){
    if (i % 2 == 1){
      ans = max(ans, sum + A[i]);
    }
    pq.push(A[i]);
    sum += A[i];
    if (pq.size() >= K){
      sum -= pq.top();
      pq.pop();
    }
  }
  cout << ans << endl;
}