import java.util.*;
class Main {
public static int [] dR = {-1, 0, 1, 0};
public static int [] dC = {0, 1, 0, -1};
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);
int maxDist = 0;
while (queue.isEmpty() == false) {
Pair curPair = queue.poll();
int cRow = curPair.row;
int cColumn = curPair.column;
int curDist = distances[cRow][cColumn];
maxDist = Math.max(maxDist, curDist);
char curChar = grid[cRow][cColumn];
for (int i = 0; i < 4; i++) {
int nextRow = cRow + dR[i];
int nextColumn = cColumn + dC[i];
if (nextRow >= rows || nextColumn >= columns || nextRow < 0 || nextColumn < 0) {
continue;
}
if (grid[nextRow][nextColumn] == '.') {
continue;
}
if (grid[nextRow][nextColumn] == curChar) {
if (curDist < distances[nextRow][nextColumn]) {
distances[nextRow][nextColumn] = curDist;
Pair addingPair = new Pair (nextRow, nextColumn);
queue.add(addingPair);
}
}
else {
if (curDist + 1 < distances[nextRow][nextColumn]) {
distances[nextRow][nextColumn] = curDist + 1;
Pair addingPair = new Pair (nextRow, nextColumn);
queue.add(addingPair);
}
}
}
}
System.out.println(maxDist);
}
private static class Pair {
int row;
int column;
public Pair (int row, int column) {
this.row = row;
this.column = column;
}
}
}
