#include <algorithm>
#include <cmath>
#include <cstdio>
#include <functional>
#include <iomanip>
#include <iostream>
#include <map>
#include <numeric>
#include <queue>
#include <set>
#include <stack>
#include <string>
#include <vector>
using namespace std;
using ll = long long;
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>> pq;
  for(int i = n - 1; i >= 0; i--) {
    if(i % 2 == 1) {
      ans = max(ans, sum + a[i]);
    }
    sum += a[i];
    pq.push(a[i]);
    if(pq.size() >= k) {
      sum -= pq.top();
      pq.pop();
    }
  }
  cout << ans << endl;
  return 0;
}