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

using i64 = long long;

int main() {
    cin.tie(nullptr)->sync_with_stdio(false);

    auto solve = [&]() {
        int n, k;
        cin >> n >> k;

        vector<int> a(n);
        vector<i64> b(n + 1);
        for (int i = 0; i < n; i++) {
            cin >> a[i];
            b[i + 1] = b[i] + a[i];
        }

        constexpr i64 inf = 4e18;
        i64 ans = -inf;

        priority_queue<i64> h;
        i64 sum = 0;

        for (int i = 1; i <= n; i++) {
            if (i >= k) {
                ans = max(ans, k * b[i] - sum);
            }
            h.push(b[i]);
            sum += b[i];
            if (h.size() == k) {
                sum -= h.top();
                h.pop();
            }
        }

        cout << ans << '\n';
    };
    
    solve();
    
    return 0;
}