Broken Dreams

You are given a string $S$ of length $N$, containing lowercase Latin letters. You are also given an integer $K$. You would like to create a new string $S'$ by following the following process: - First, partition $S$ into exactly $K$ non-empty [subsequences](https://en.wikipedia.org/wiki/Subsequence) $S_1, S_2, \ldots, S_K$. Note that every character of $S$ must be present in exactly one of the $S_