import java.util.*;
import java.io.*;
public class tracks {
public static void main(String[] args) throws IOException {
BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
PrintWriter out = new PrintWriter(System.out);
StringTokenizer in = new StringTokenizer(br.readLine());
int h = Integer.parseInt(in.nextToken()), w = Integer.parseInt(in.nextToken());
int[][] grid = new int[h][w];
for (int i=0; i< h; i++) {
String s = br.readLine();
for (int j =0; j< w; j++) grid[i][j] = s.charAt(j);
}
ArrayDeque<int[]> next = new ArrayDeque<>();
next.addLast(new int[] {0,0,1});
int maxV = 1;
while (!next.isEmpty()) {
int[] vals = next.removeFirst();
int r = vals[0], c = vals[1], v = vals[2];
maxV = Math.max(maxV, v);
if (r < h-1 && grid[r+1][c] != '.') {
if (grid[r+1][c]==grid[r][c]) {
next.addFirst(new int[] {r+1,c,v});
} else {
next.addLast(new int[] {r+1,c,v+1});
}
}
if (r > 0 && grid[r-1][c] != '.') {
if (grid[r-1][c]==grid[r][c]) {
next.addFirst(new int[] {r-1,c,v});
} else {
next.addLast(new int[] {r-1,c,v+1});
}
}
if (c < w-1 && grid[r][c+1] != '.') {
if (grid[r][c+1]==grid[r][c]) {
next.addFirst(new int[] {r,c+1,v});
} else {
next.addLast(new int[] {r,c+1,v+1});
}
}
if (c > 0 && grid[r][c-1] != '.') {
if (grid[r][c-1]==grid[r][c]) {
next.addFirst(new int[] {r,c-1,v});
} else {
next.addLast(new int[] {r,c-1,v+1});
}
}
grid[r][c] = '.';
}
out.println(maxV);
br.close();
out.close();
}
}
