#include <iostream>
#include <vector>
#include <cmath>
#include <map>
#include <set>
#include <iomanip>
#include <queue>
#include <algorithm>
#include <numeric>
#include <deque>
#include <complex>
#include <cassert>

using namespace std;
using ll = long long;

int main(){

    ll N, K, S=0, ans=0, mi;
    cin >> N >> K;
    multiset<ll> st;
    vector<ll> A(N);

    for (int i=0; i<N; i++) cin >> A[i];
    for (int i=N-1; i>=0; i--){
        if (i % 2 == 1){
            if (st.size() == K-1){
                ans = max(ans, A[i]+S);
            }
        }
        st.insert(A[i]);
        S += A[i];
        if (st.size() == K){
            S -= *st.begin();
            st.erase(st.begin());
        }
    }

    cout << ans << endl;

    return 0;
}