#include <iostream>
#include <string>
#include <vector>
#include <algorithm>
#include <functional>
#include <cmath>
#include <iomanip>
#include <stack>
#include <queue>
#include <numeric>
#include <map>
#include <unordered_map>
#include <set>
#include <fstream>
#include <chrono>
#include <random>
#include <bitset>
//#include <atcoder/all>
#include <sstream>
#define rep(i,n) for(int i=0;i<(n);i++)
#define all(x) x.begin(), x.end()
#define rall(x) x.rbegin(), x.rend()
#define sz(x) ((int)(x).size())
#define pb push_back
using ll = long long;
using namespace std;
template<class T>bool chmax(T &a, const T &b) { if (a<b) { a=b; return 1; } return 0; }
template<class T>bool chmin(T &a, const T &b) { if (b<a) { a=b; return 1; } return 0; }
ll gcd(ll a, ll b) {return b?gcd(b,a%b):a;}
ll lcm(ll a, ll b) {return a/gcd(a,b)*b;}

int main(){
  int N,K; cin >> N >> K;
  vector<ll> A(N); rep(i,N) cin >> A[i];
  ll s=0;
  ll ans = 0;
  multiset<ll> ms;
  for(int i=N-1;i>=0;i--){
    if(sz(ms)==K-1&&i%2==1){
      chmax(ans,A[i]+s);
    }
    ms.insert(A[i]);
    s+=A[i];
    if(sz(ms)==K){
      ll b = *ms.begin();
      s-=b;
      ms.erase(ms.begin());
    }
  }
  cout << ans << endl;
  return 0;
}