A12587 | 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.

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$ ).

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