A to B (Easy)

**This is the easy version of the problem. Here, you only need to output the minimum cost only.** You are given $2$ binary strings $A$ and $B$, both of length $N$. You can perform the following operation on $A$ multiple times (possibly $0$): - Choose $L$ and $R$ such that $1 \le L \le R \le N$, and flip all the values $A_L, A_{L + 1}, \ldots, A_R$. - The cost of this operation is $1$ if $A_L =