CF1175D.Array Splitting

You are given an array $a_1, a_2, \dots, a_n$ and an integer $k$.

You are asked to divide this array into $k$ non-empty consecutive subarrays. Every element in the array should be included in exactly one subarray. Let $f(i)$ be the index of subarray the $i$-th element belongs to. Subarrays are numbered from left to right and from $1$ to $k$.

Let the cost of division be equal to $\sum\limits_{i=1}^{n} (a_i \cdot f(i))$. For example, if $a = [1, -2, -3, 4, -5, 6, -7]$ and we divide it into $3$ subbarays in the following way: $[1, -2, -3], [4, -5], [6, -7]$, then the cost of division is equal to $1 \cdot 1 - 2 \cdot 1 - 3 \cdot 1 + 4 \cdot 2 - 5 \cdot 2 + 6 \cdot 3 - 7 \cdot 3 = -9$.

Calculate the maximum cost you can obtain by dividing the array $a$ into $k$ non-empty consecutive subarrays.

给你一个数组 $a_1, a_2, \dots, a_n$ 和一个整数 $k$。

你需要将该数组划分为 $k$ 个非空且连续的子数组。数组中的每个元素必须且仅被包含在其中一个子数组中。令 $f(i)$ 表示第 $i$ 个元素所属子数组的编号。子数组从左到右依次编号，编号范围为 $1$ 到 $k$。

定义划分的代价为 $\sum\limits_{i=1}^{n} (a_i \cdot f(i))$。例如，若 $a = [1, -2, -3, 4, -5, 6, -7]$，并将它按如下方式划分为 $3$ 个子数组：$[1, -2, -3], [4, -5], [6, -7]$，则划分的代价为
$1 \cdot 1 - 2 \cdot 1 - 3 \cdot 1 + 4 \cdot 2 - 5 \cdot 2 + 6 \cdot 3 - 7 \cdot 3 = -9$。

请计算将数组 $a$ 划分为 $k$ 个非空连续子数组所能得到的最大代价。

The first line contains two integers $n$ and $k$ ($1 \le k \le n \le 3 \cdot 10^5$).

The second line contains $n$ integers $a_1, a_2, \dots, a_n$ ($ |a_i| \le 10^6$).

第一行包含两个整数 $n$ 和 $k$（$1 \le k \le n \le 3 \cdot 10^5$）。

第二行包含 $n$ 个整数 $a_1, a_2, \dots, a_n$（$|a_i| \le 10^6$）。

Print the maximum cost you can obtain by dividing the array $a$ into $k$ nonempty consecutive subarrays.

输出将数组 $a$ 划分为 $k$ 个非空连续子数组所能获得的最大代价。