CF533E.Correcting Mistakes

Analyzing the mistakes people make while typing search queries is a complex and an interesting work. As there is no guaranteed way to determine what the user originally meant by typing some query, we have to use different sorts of heuristics.

Polycarp needed to write a code that could, given two words, check whether they could have been obtained from the same word as a result of typos. Polycarpus suggested that the most common typo is skipping exactly one letter as you type a word.

Implement a program that can, given two distinct words S and T of the same length n determine how many words W of length n + 1 are there with such property that you can transform W into both S, and T by deleting exactly one character. Words S and T consist of lowercase English letters. Word W also should consist of lowercase English letters.

分析人们在输入搜索查询时所犯的错误是一项复杂而有趣的任务。由于无法保证准确判断用户输入某个查询时原本想表达的含义，我们必须采用各种启发式方法。

波利卡普需要编写一段代码，使其能够针对两个单词，判断它们是否可能由同一个原始单词经打字错误产生。波利卡普认为，最常见的打字错误是在输入单词时恰好漏掉一个字母。

请实现一个程序：给定两个长度均为 $n$ 的不同单词 $S$ 和 $T$，求满足如下性质的长度为 $n+1$ 的单词 $W$ 的个数：通过从 $W$ 中恰好删除一个字符，既可以得到 $S$，也可以得到 $T$。单词 $S$ 和 $T$ 仅由小写英文字母组成；单词 $W$ 同样也必须仅由小写英文字母组成。

The first line contains integer n (1 ≤ n ≤ 100 000) — the length of words S and T.

The second line contains word S.

The third line contains word T.

Words S and T consist of lowercase English letters. It is guaranteed that S and T are distinct words.

第一行包含一个整数 $n$（$1 \leq n \leq 100\,000$）—— 即字符串 $S$ 和 $T$ 的长度。

第二行包含字符串 $S$。

第三行包含字符串 $T$。

字符串 $S$ 和 $T$ 仅由小写英文字母组成。保证 $S$ 和 $T$ 是两个不同的字符串。

Print a single integer — the number of distinct words W that can be transformed to S and T due to a typo.

输出一个整数——由于拼写错误，能够被转换为 S 和 T 的不同单词 W 的数量。

In the first sample test the two given words could be obtained only from word "treading" (the deleted letters are marked in bold).

In the second sample test the two given words couldn't be obtained from the same word by removing one letter.

In the third sample test the two given words could be obtained from either word "tory" or word "troy".

在第一个样例测试中，给定的两个单词只能由单词 “treading” 删除字母得到（被删除的字母以粗体标出）。

在第二个样例测试中，给定的两个单词无法通过从同一个单词中删除一个字母而同时得到。

在第三个样例测试中，给定的两个单词可由单词 “tory” 或单词 “troy” 删除字母得到。