#include <iostream>
#include <queue>
using namespace std;
typedef long long ll;

int main()
{
    int n, k;
    cin >> n >> k;
    int a[200005];
    for(int i = 0; i < n; i++)
    {
        cin >> a[i];
    }
    ll ans = 0, s = 0;
    priority_queue<int, vector<int>, greater<int>> que;
    for(int i = n - 1; i >= 0; i--)
    {
        if(i % 2)
        {
            ans = max(ans, a[i] + s);
        }
        s += a[i];
        que.push(a[i]);
        if((int)que.size() >= k)
        {
            s -= que.top();
            que.pop();
        }
    }
    cout << ans << endl;
}