1140C - Playlist

using namespace std;
using ll = long long;
struct Song {
  ll length;
  ll beauty;
  bool operator<(const Song &s) const { return (beauty < s.beauty); }
};
int n, k;
Song songs[300100];
ll max_pleasure(void) {
  ll ans = 0, cur = 0, len = 0;
  priority_queue<ll, vector<ll>, greater<ll>> pq;
  sort(songs, songs + n);
  for (int i = n - 1; i >= 0; --i) {
    len += songs[i].length;
    if (pq.size() == k) {
      len -= pq.top();
      pq.pop();
    }
    pq.push(songs[i].length);
    cur = len * songs[i].beauty;
    ans = max(ans, cur);
  }
  return ans;
}
int main(void) {
  cin >> n >> k;
  for (int i = 0; i < n; ++i) {
    cin >> songs[i].length;
    cin >> songs[i].beauty;
  }
  cout << max_pleasure() << endl;
  return 0;
}