#include <bits/stdc++.h>
#define F first
#define S second
#define all(x) begin(x), end(x)
#define pb push_back
#define FOR(i, a, b) for (int i = (a); i <= (b); i++)
#ifdef LOCAL
#define HEHE freopen("in.txt", "r", stdin);
#define debug(HEHE...) cerr << #HEHE << " = ", dout(HEHE)
void dout() { std::cerr << '\n'; }
template <typename T, typename ...U>
void dout(T t, U ...u) { std::cerr << t << ' '; dout(u...); }
#else
#define HEHE ios_base::sync_with_stdio(0), cin.tie(0);
#define debug(...) 7122
#endif
using namespace std;

#define chmax(a, b) (a) = (a) > (b) ? (a) : (b)
#define chmin(a, b) (a) = (a) < (b) ? (a) : (b)

#define int long long

signed main() {
    HEHE
    int n, k;
    cin >> n >> k;
    vector<int> a(n + 1);
    FOR (i, 1, n) cin >> a[i];
    partial_sum(all(a), begin(a));
    priority_queue<int> pq;
    int ans = INT64_MIN, cur = 0;
    FOR (i, 2, k) pq.push(a[i - 1]), cur -= a[i - 1];
    chmax(ans, a[k] * k + cur);
    FOR (i, k + 1, n) {
        pq.push(a[i - 1]);
        cur -= a[i - 1];
        cur += pq.top(); pq.pop();
        chmax(ans, a[i] * k + cur);
    }
    cout << ans << '\n';
}