CF1140C.Playlist

You have a playlist consisting of $n$ songs. The $i$-th song is characterized by two numbers $t_i$ and $b_i$ — its length and beauty respectively. The pleasure of listening to set of songs is equal to the total length of the songs in the set multiplied by the minimum beauty among them. For example, the pleasure of listening to a set of $3$ songs having lengths $[5, 7, 4]$ and beauty values $[11, 14, 6]$ is equal to $(5 + 7 + 4) \cdot 6 = 96$.

You need to choose at most $k$ songs from your playlist, so the pleasure of listening to the set of these songs them is maximum possible.

你有一个包含 $n$ 首歌曲的播放列表。第 $i$ 首歌曲由两个数 $t_i$ 和 $b_i$ 描述——分别表示其长度和美感值。聆听一组歌曲所带来的愉悦感，等于该组中所有歌曲长度之和乘以其中最小的美感值。例如，聆听一组包含 $3$ 首歌曲（长度分别为 $[5, 7, 4]$，美感值分别为 $[11, 14, 6]$）所带来的愉悦感为 $(5 + 7 + 4) \cdot 6 = 96$。

你需要从播放列表中至多选择 $k$ 首歌曲，使得聆听这些歌曲所获得的愉悦感尽可能大。

The first line contains two integers $n$ and $k$ ($1 \le k \le n \le 3 \cdot 10^5$) – the number of songs in the playlist and the maximum number of songs you can choose, respectively.

Each of the next $n$ lines contains two integers $t_i$ and $b_i$ ($1 \le t_i, b_i \le 10^6$) — the length and beauty of $i$-th song.

第一行包含两个整数 $n$ 和 $k$（$1 \le k \le n \le 3 \cdot 10^5$）—— 分别表示播放列表中歌曲的数量以及你最多可选择的歌曲数量。

接下来的 $n$ 行，每行包含两个整数 $t_i$ 和 $b_i$（$1 \le t_i, b_i \le 10^6$）—— 分别表示第 $i$ 首歌的时长和悦耳度。

Print one integer — the maximum pleasure you can get.

输出一个整数——你能获得的最大愉悦值。

In the first test case we can choose songs ${1, 3, 4}$, so the total pleasure is $(4 + 3 + 6) \cdot 6 = 78$.

In the second test case we can choose song $3$. The total pleasure will be equal to $100 \cdot 100 = 10000$.

在第一个测试用例中，我们可以选择歌曲 $\{1, 3, 4\}$，因此总愉悦值为 $(4 + 3 + 6) \cdot 6 = 78$。

在第二个测试用例中，我们可以选择歌曲 $3$。总愉悦值将等于 $100 \cdot 100 = 10000$。