import java.util.*;
import java.io.*;
public class tracks {
private static int[] dx = {0, 0, -1, 1};
private static int[] dy = {-1, 1, 0, 0};
private static int n, m;
private static boolean check(int x, int y){
return 0 <= x && x < n && 0 <= y && y < m;
}
public static void main(String[] args) throws IOException{
BufferedReader r = new BufferedReader(new InputStreamReader(System.in));
PrintWriter pw = new PrintWriter(System.out);
StringTokenizer st = new StringTokenizer(r.readLine());
n = Integer.parseInt(st.nextToken()); m = Integer.parseInt(st.nextToken());
char[][] grid = new char[n][m];
for (int i = 0; i < n; i++) {
String s = r.readLine();
for (int j = 0; j < m; j++) {
grid[i][j] = s.charAt(j);
}
}
int[][] ans = new int[n][m];
ans[0][0] = 1;
Deque<int[]> cur = new LinkedList<>();
cur.add(new int[]{0, 0});
int z = -1;
while(!cur.isEmpty()){
int[] x = cur.poll();
z = Math.max(z, ans[x[0]][x[1]]);
for (int i = 0; i < 4; i++) {
int fx = x[0] + dx[i];
int fy = x[1] + dy[i];
if(check(fx, fy) && ans[fx][fy] == 0){
if(grid[x[0]][x[1]] == grid[fx][fy]){
ans[fx][fy] = ans[x[0]][x[1]];
cur.addFirst(new int[]{fx, fy});
}
else if(grid[fx][fy] != '.'){
ans[fx][fy] = ans[x[0]][x[1]] + 1;
cur.addLast(new int[]{fx, fy});
}
}
}
}
pw.println(z);
pw.close();
}
}
