//package bfs;
import java.io.*;
import java.util.*;
class tracks {
public static void main(String[] args) throws IOException {
tracks obj = new tracks();
obj.doStuff();
}
private void doStuff() throws IOException {
BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
StringTokenizer st = new StringTokenizer(br.readLine());
char[][] grid = new char[Integer.parseInt(st.nextToken())][Integer.parseInt(st.nextToken())];
int[][] vis = new int[grid.length][grid[0].length];
for (int i = 0; i < grid.length; i++) {
grid[i] = br.readLine().toCharArray();
}
br.close();
vis[0][0] = 1;
ArrayDeque<int[]> q = new ArrayDeque<>();
q.add(new int[] {0, 0});
int[] yinc = new int[] {-1, 0, 1, 0};
int[] xinc = new int[] {0, 1, 0, -1};
int max = 1;
while (!q.isEmpty()) {
int[] next = q.poll();
char thisChar = grid[next[0]][next[1]];
int thisDist = vis[next[0]][next[1]];
// first is y, second is x
for (int i = 0; i < 4; i++) {
int nexty = next[0]+yinc[i];
int nextx = next[1]+xinc[i];
if (nexty < 0 || nexty >= grid.length) continue;
if (nextx < 0 || nextx >= grid[0].length) continue;
if (vis[nexty][nextx] == 0 && grid[nexty][nextx] != '.') {
if (grid[nexty][nextx] != thisChar) {
vis[nexty][nextx] = thisDist+1;
max = Math.max(max, thisDist+1);
q.add(new int[] {nexty, nextx});
} else {
vis[nexty][nextx] = thisDist;
q.push(new int[] {nexty, nextx});
}
}
}
}
System.out.println(max);
}
}
