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

const ll INF = 8000000000000000000;

int main()
{
    int n, k;
    cin >> n >> k;
    priority_queue<ll, vector<ll>, greater<ll>> que;
    ll s;
    cin >> s;
    if (n == 1)
    {
        cout << s << endl;
        return 0;
    }
    ll x = s;
    ll ans = -INF;
    for (int i = 1; i < n; i++)
    {
        ll a;
        cin >> a;
        que.push(-s);
        s += a;
        x += a * ((int)que.size() + 1);
        if (i >= k)
        {
            ll t = que.top();
            x -= s + t;
            que.pop();
        }
        if ((int)que.size() == k - 1)
        {
            ans = max(ans, x);
        }
    }
    cout << ans << endl;
}