#include <bits/stdc++.h>
using namespace std;
typedef long long ll;
template<class T>bool chmax(T &a, const T &b) { if (a<b) { a=b; return true; } return false; }
template<class T>bool chmin(T &a, const T &b) { if (b<a) { a=b; return true; } return false; }
#define all(x) (x).begin(),(x).end()
#define fi first
#define se second
#define mp make_pair
#define si(x) int(x.size())
const int mod=998244353,MAX=200005,INF=1<<30;

int main(){
    
    std::ifstream in("text.txt");
    std::cin.rdbuf(in.rdbuf());
    cin.tie(0);
    ios::sync_with_stdio(false);
    
    int N,K;cin>>N>>K;
    vector<ll> A(N);
    for(int i=0;i<N;i++){
        cin>>A[i];
    }
    
    priority_queue<ll,vector<ll>,greater<ll>> PQ;
    ll sum=0;
    
    ll ans=0;
    
    for(int i=N-1;i>=0;i--){
        if(i&1){
            chmax(ans,A[i]+sum);
        }
        PQ.push(A[i]);
        sum+=A[i];
        if(si(PQ)>=K){
            sum-=PQ.top();
            PQ.pop();
        }
    }
    
    cout<<ans<<endl;
    
}