#include <iostream>
#include <string>
#include <vector>
#include <algorithm>
#include <queue>
#include <atcoder/modint>

using namespace std;
using i32 = int32_t;
using u32 = uint32_t;
using i64 = int64_t;
using u64 = uint64_t;
#define rep(i,n) for(int i=0; i<(int)(n); i++)


const i64 INF = 1001001001001001001;
using modint = atcoder::static_modint<998244353>;

int main(){
    int N; cin >> N;
    int K; cin >> K;
    vector<int> A(N);
    rep(i,N) cin >> A[i];
    priority_queue<i64, vector<i64>, greater<i64>> Que;
    i64 queSum = 0;
    i64 ans = 0;
    for(int i=N-1; i>=0; i--){
        if(i%2 == 1 && Que.size() == K-1){
            ans = max(ans, queSum + A[i]);
        }
        Que.push(A[i]);
        queSum += A[i];
        if(Que.size() > K-1){
            queSum -= Que.top();
            Que.pop();
        }
    }
    cout << ans << '\n';
    return 0;
}


struct ios_do_not_sync{
    ios_do_not_sync(){
        std::ios::sync_with_stdio(false);
        std::cin.tie(nullptr);
    }
} ios_do_not_sync_instance;