Swap and Unite

You have a string $S$ consisting of lowercase letters. You can perform the following operation on $S$: - Choose two indices $i$ and $j$ ($1 \leq i \lt j \leq |S|$), and swap $S_i$ and $S_j$. For example, if $S = \texttt{codechef}$, choosing $i = 3$ and $j = 6$ results in the string $\texttt{cohecdef}$. You've always liked unity. To this end, find the **minimum** number of operations required s