import java.util.*;
class Main {
public static void main (String[]args) {
Scanner scan = new Scanner (System.in);
int rows = scan.nextInt();
int columns = scan.nextInt();
char [][] grid = new char [rows][columns];
for (int i = 0; i < rows; i++) {
String line = scan.next();
for (int j = 0; j < columns; j++) {
grid[i][j] = line.charAt(j);
}
}
int [][] distances = new int [rows][columns];
for (int i = 0; i < rows; i++) {
Arrays.fill(distances[i], Integer.MAX_VALUE);
}
distances[0][0] = 1;
Queue <Pair> queue = new LinkedList <Pair>();
Pair startingPair = new Pair (0, 0);
queue.add(startingPair);
while (queue.isEmpty() == false) {
Pair curPair = queue.poll();
int cRow = curPair.row;
int cColumn = curPair.column;
int curDist = distances[cRow][cColumn];
char curChar = grid[cRow][cColumn];
if (cRow - 1 >= 0) {
if (grid[cRow - 1][cColumn] == curChar) {
if (curDist < distances[cRow - 1][cColumn]) {
distances[cRow - 1][cColumn] = curDist;
Pair addingPair = new Pair (cRow - 1, cColumn);
queue.add(addingPair);
}
}
else {
if (curDist + 1 < distances[cRow - 1][cColumn]) {
distances[cRow - 1][cColumn] = curDist + 1;
Pair addingPair = new Pair (cRow - 1, cColumn);
queue.add(addingPair);
}
}
}
if (cColumn + 1 < columns) {
if (grid[cRow][cColumn + 1] == curChar) {
if (curDist < distances[cRow][cColumn + 1]) {
distances[cRow][cColumn + 1] = curDist;
Pair addingPair = new Pair (cRow, cColumn + 1);
queue.add(addingPair);
}
}
else {
if (curDist + 1 < distances[cRow][cColumn + 1]) {
distances[cRow][cColumn + 1] = curDist + 1;
Pair addingPair = new Pair (cRow, cColumn + 1);
queue.add(addingPair);
}
}
}
if (cRow + 1 < rows) {
if (grid[cRow + 1][cColumn] == curChar) {
if (curDist < distances[cRow + 1][cColumn]) {
distances[cRow + 1][cColumn] = curDist;
Pair addingPair = new Pair (cRow + 1, cColumn);
queue.add(addingPair);
}
}
else {
if (curDist + 1 < distances[cRow + 1][cColumn]) {
distances[cRow + 1][cColumn] = curDist + 1;
Pair addingPair = new Pair (cRow + 1, cColumn);
queue.add(addingPair);
}
}
}
if (cColumn - 1 >= 0) {
if (grid[cRow][cColumn - 1] == curChar) {
if (curDist < distances[cRow][cColumn - 1]) {
distances[cRow][cColumn - 1] = curDist;
Pair addingPair = new Pair (cRow, cColumn - 1);
queue.add(addingPair);
}
}
else {
if (curDist + 1 < distances[cRow][cColumn - 1]) {
distances[cRow][cColumn - 1] = curDist + 1;
Pair addingPair = new Pair (cRow, cColumn - 1);
queue.add(addingPair);
}
}
}
}
int maxDist = 0;
for (int i = 0; i < rows; i++) {
for (int j = 0; j < columns; j++) {
maxDist = Math.max(maxDist, distances[i][j]);
}
}
System.out.println(maxDist);
}
private static class Pair {
int row;
int column;
public Pair (int row, int column) {
this.row = row;
this.column = column;
}
}
}
