#include <bits/stdc++.h>
#define rep(i,n) for(int i = 0; i < (n); i++)
using namespace std;
typedef long long ll;

int main(){
    cin.tie(0);
    ios::sync_with_stdio(0);
    
    int N,K; cin >> N >> K;
    vector<int> A(N);
    rep(i,N) cin >> A[i];

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