#if __INCLUDE_LEVEL__ == 0

#include __BASE_FILE__

void Solve() {
  int n, k;
  IN(n, k);
  vector<int64_t> a(n);
  IN(a);

  vector<int64_t> suff(n + 1);
  for (int i : Rev(Rep(0, n))) {
    suff[i] = a[i] + suff[i + 1];
  }

  int k1 = k - 1;
  int64_t ans = -INF64;

  int64_t sum = 0;
  priority_queue q(greater{}, vector<int64_t>{});
  for (int i : Rep1(1, n)) {
    if (Sz(q) == k1) {
      int64_t cur = suff[0] + sum - suff[i] * k;
      SetMax(ans, cur);
    }
    q.push(suff[i]);
    sum += suff[i];
    if (Sz(q) > k1) {
      sum -= q.top();
      q.pop();
    }
  }

  OUT(ans);
}

// | 1 | 2 | 3 | 0 |
// 1, ..., 1, -k
// 先頭は必ず選ぶ

int main() {
  ios::sync_with_stdio(false);
  cin.tie(nullptr);

  Solve();
}

#elif __INCLUDE_LEVEL__ == 1

#include <bits/stdc++.h>

template <class T> concept MyRange = std::ranges::range<T> && !std::convertible_to<T, std::string_view>;
template <class T> concept MyTuple = std::__is_tuple_like<T>::value && !MyRange<T>;

namespace std {

istream& operator>>(istream& is, MyRange auto&& r) {
  for (auto&& e : r) is >> e;
  return is;
}
istream& operator>>(istream& is, MyTuple auto&& t) {
  apply([&](auto&... xs) { (is >> ... >> xs); }, t);
  return is;
}

ostream& operator<<(ostream& os, MyRange auto&& r) {
  auto sep = "";
  for (auto&& e : r) os << exchange(sep, " ") << e;
  return os;
}
ostream& operator<<(ostream& os, MyTuple auto&& t) {
  auto sep = "";
  apply([&](auto&... xs) { ((os << exchange(sep, " ") << xs), ...); }, t);
  return os;
}

}  // namespace std

using namespace std;

#define LAMBDA2(x, y, ...) ([&](auto&& x, auto&& y) -> decltype(auto) { return __VA_ARGS__; })
#define Rev views::reverse
#define Rep(...) [](int l, int r) { return views::iota(min(l, r), r); }(__VA_ARGS__)
#define Rep1(...) [](int l, int r) { return Rep(l, r + 1); }(__VA_ARGS__)
#define Sz(r) int(size(r))
#define SetMax(...) LAMBDA2(x, y, x < y && (x = y, 1))(__VA_ARGS__)
#define INF64 (INT64_MAX / 2)
#define IN(...) (cin >> forward_as_tuple(__VA_ARGS__))
#define OUT(...) (cout << forward_as_tuple(__VA_ARGS__) << '\n')

#endif  // __INCLUDE_LEVEL__ == 1