201104: [AtCoder]ARC110 E - Shorten ABC

Problem Statement

We have a string $S$ of length $N$ consisting of A, B, and C.

You can do the following operation on $S$ zero or more times:

• Choose $i$ $(1 \leq i \leq |S| - 1)$ such that $S_i \neq S_{i + 1}$. Replace $S_i$ with the character (among A, B, and C) that is different from both $S_i$ and $S_{i + 1}$, and remove $S_{i + 1}$ from $S$.

Find the number of distinct strings that $S$ can be after zero or more operations, and print the count modulo $(10^9+7)$.

Constraints

• $1 \leq N \leq 10^6$
• $S$ is a string of length $N$ consisting of A, B, and C.

Input

Input is given from Standard Input in the following format:

$N$
$S$

Output

Print the number of distinct strings that $S$ can be after zero or more operations, modulo $(10^9+7)$.

Sample Input 1

5
ABAAC

Sample Output 1

11

For example, the following sequence of operations turns $S$ into ACB:

• First, choose $i=2$. We replace $S_2$ with C and remove $S_3$, turning $S$ into ACAC.
• Then, choose $i=3$. We replace $S_3$ with B and remove $S_4$, turning $S$ into ACB.

Sample Input 2

50
AACCCCBBBACCCCABABCCCCABACCACACACCACABABBBABABACCB

Sample Output 2

256972022