Alan Challenges Christopher

Alan and Christopher are playing a game. There is a string $S$ of length $N$. Alan gives two integers $L$ and $R$ to Christopher. Consider the substring from $Lth$ to $Rth$ character of $S$. (Both inclusive) Christopher is supposed to reconstruct this substring using the characters in $S$, except he is not allowed to pick them from the positions $L$ to $R$. (Both inclusive) Note that