Continuous Sum

You are given an array $a$ with $n$ integers. You can perform the following operation at most $k$ times: - Choose two indices i and j, in which $i$ $mod$ $k$ = $j$ $mod$ $k$ $(1 ≤ i < j ≤ n)$. - swap $a[i]$ and $a[j]$. After performing all operations, you have to select $k$ consecutive elements, and the sum of the $k$ elements becomes your score. Find the maximum score you can get. Here $x$ $mo