CF1012D AB-Strings

## 题面描述 给定两个只包含 $\texttt{a}$ 和 $\texttt{b}$ 的字符串，每次操作可以把两个字符串的任意前缀进行交换（前缀长度可以为 $0$），问最少多少次操作可以使的一个串只有 $\texttt{a}$，另一个串只有 $\texttt{b}$。

两行，一行一个字符串，保证串长 $\leq 200000$。 保证两个串中有 $\texttt{a}$ 和 $\texttt{b}$。

第一行一个整数 $n(0\leq n\leq 500000)$，表示答案。 后面 $n$ 行，一行两个整数，表示每次操作时被交换的两个串的前缀长度。

In the first example, you can solve the problem in two operations: 1. Swap the prefix of the first string with length $ 1 $ and the prefix of the second string with length $ 0 $ . After this swap, you'll have strings ab and bbb. 2. Swap the prefix of the first string with length $ 1 $ and the prefix of the second string with length $ 3 $ . After this swap, you'll have strings bbbb and a. In the second example, the strings are already appropriate, so no operations are needed.