Construct String

Consider a string $S$ consisting of lowercase Latin alphabets. In one operation, you can pick an index from string $S$ and replace the character at that index with $3$ occurrences of the same character. For example, if $S = \texttt{dabc}$, in one operation, we can choose the index $2$ and replace $S_2$ with $3$ occurrences of $S_2$. Thus, the string becomes $S =\texttt{d} \underline{\texttt{aa