1393D · Rarity and New Dress

Problem: Carousel Boutique is busy again! Rarity has decided to visit the pony ball and she surely needs a new dress, because going out in the same dress several times is a sign of bad manners. First of all, she needs a dress pattern, which she is going to cut out from the rectangular piece of the multicolored fabric.

The piece of the multicolored fabric consists of $n \times m$ separate square scraps. Since Rarity likes dresses in style, a dress pattern must only include scraps sharing the same color. A dress pattern must be the square, and since Rarity is fond of rhombuses, the sides of a pattern must form a $45^{\circ}$ angle with sides of a piece of fabric (that way it will be resembling the traditional picture of a rhombus).

Examples of proper dress patterns: Examples of improper dress patterns: The first one consists of multi-colored scraps, the second one goes beyond the bounds of the piece of fabric, the third one is not a square with sides forming a $45^{\circ}$ angle with sides of the piece of fabric.

Rarity wonders how many ways to cut out a dress pattern that satisfies all the conditions that do exist. Please help her and satisfy her curiosity so she can continue working on her new masterpiece!

Input Format: The first line contains two integers $n$ and $m$ ($1 \le n, m \le 2000$). Each of the next $n$ lines contains $m$ characters: lowercase English letters, the $j$-th of which corresponds to scrap in the current line and in the $j$-th column. Scraps having the same letter share the same color, scraps having different letters have different colors.

Output Format: Print a single integer: the number of ways to cut out a dress pattern to satisfy all of Rarity's conditions.

Note: In the first example, all the dress patterns of size $1$ and one of size $2$ are satisfactory.

In the second example, only the dress patterns of size $1$ are satisfactory.