描述：

A single-player game is played on a rectangular board divided in R rows and C columns. There is a single uppercase letter (A-Z) written in every position in the board.
Before the begging of the game there is a figure in the upper-left corner of the board (first row, first column). In every move, a player can move the figure to the one of the adjacent positions (up, down,left or right). Only constraint is that a figure cannot visit a position marked with the same letter twice.
The goal of the game is to play as many moves as possible.
Write a program that will calculate the maximal number of positions in the board the figure can visit in a single game.

输入：

The first line of the input contains two integers R and C, separated by a single blank character, 1 <= R, S <= 20.
The following R lines contain S characters each. Each line represents one row in the board.

输出：

The first and only line of the output should contain the maximal number of position in the board the figure can visit.

样例输入：

3 6

HFDFFB

AJHGDH

DGAGEH

样例输出：

6

翻译：

字母

描述：

一个玩家的游戏就是在一个R行C列的木板上进行的。有一个字母（A-Z）被写在木板的每个位置上。

在游戏开始时有一个数字在木板的左上角（第一行第一列）。在每次的移动中，一个玩家能够移动一个数字到这四个中的一个位置（上下左右）。唯一矛盾的是同一个字母不能够到同一个位置两次。这个游戏的目的就是去尽可能多的移动。

写出一个程序能够计算出在木板上移动数字的最大值。

输入：

第一行输入包括两个整数R和C，被一个空格分隔开。R>=1,S<=20.

接下来每R行包含S个输出。每行就代表，木板上的一行。

输出：

第一行和输出的一行应该包含木板上的最大的位置。

样例输入：

3 6

HFDFFB

AJHGDH

DGAGEH

样例输出：

6