String Operations

Two strings $A$ and $B$ are *equivalent* (denoted by $A \sim B$) if they have the same lengths and $A$ can be transformed into $B$ by performing the following operation zero or more times: choose a substring of $A$ which contains '1' an even number of times and reverse this substring. You are given a binary string $S$. Find the number of different equivalence classes of the substrings of this s