#include <bits/stdc++.h>
#include <atcoder/all>
using namespace std;
using namespace atcoder;
using mint = modint998244353;
using ll = long long;
#define all(x) x.begin(), x.end()
#define rep(i, n) for (int i = 0; i < n; i++)
int main(void)
{
    int n, k;
    cin >> n >> k;
    vector<ll> a(n);
    rep(i, n) cin >> a[i];
    ll summ = 0;
    ll ans = 0;
    priority_queue<ll, vector<ll>, greater<ll>> q;
    for (int i = n - 1; i >= 0; i--){
        if(i % 2){
            ans = max(ans, summ + a[i]);
        }
        q.push(a[i]);
        summ += a[i];
        if(q.size() >= k){ 
            summ -= q.top();
            q.pop();
        }
    }
    cout << ans << endl;
    return 0;
}