#include <bits/stdc++.h>
using namespace std;

int main() {
    int N,K;
    cin >> N >> K;
    vector<int>A(N);
    for(int i = 0; i < N; i++) {
        cin >> A[i];
    }
    long long ans = 0,sum = 0;
    priority_queue<int,vector<int>,greater<int>>que;
    for(int i = N-1; i >= 0; i--) {
        if(i%2 == 1) {
            ans = max(ans,sum+A[i]);
        }
        sum += A[i];
        que.push(A[i]);
        if(que.size() == K) {
            sum -= que.top();
            que.pop();
        }
    }
    cout << ans << endl;
}