Delete Sorted Subsequence

The set of balanced binary strings are as follows: - The empty string is balanced. - If $S$ is balanced, then $0 + S + 1$ is balanced. - If $S, T$ are balanced, then $S + T$ is balanced. Here $+$ denotes string concatenation. For example, $01, 0101$ and $0011$ are balanced, but $10$ and $010$ are not. --- Given a binary string $S$ of length $N$, you can perform the following operation on it