#include <iostream>
#include <atcoder/segtree>
using namespace std;
typedef long long ll;

const ll INF = 100000000000000000;

using S = std::pair<ll, int>;

S op(S a, S b)
{
    return max(a, b);
}

S e()
{
    return S(-INF, -1);
}

int main()
{
    int n, k;
    cin >> n >> k;
    int a[500005];
    for (int i = 0; i < n; i++)
    {
        cin >> a[i];
    }
    ll o = 0;
    for (int i = n - 1; i >= k; i--)
    {
        o += a[i];
        if (o <= 0)
        {
            n = i;
            o = 0;
        }
    }
    ll s[500005];
    s[n] = 0;
    for (int i = n - 1; i >= 0; i--)
    {
        s[i] = s[i + 1] + a[i];
    }
    atcoder::segtree<S, op, e> seg(n);
    for (int i = 0; i < n; i++)
    {
        seg.set(i, S(s[i], i));
    }
    int r = n;
    ll ans = 0;
    for (int i = k; i > 1; i--)
    {
        int l = seg.prod(i - 1, r).second;
        ans += (s[l] - s[r]) * i;
        r = l;
    }
    ans += s[0] - s[r];
    cout << ans << endl;
}