import java.util.*;
public class tracks {
static int n, m, ans = 1;
static int[] dx = {0, 0, -1, 1}, dy = {-1, 1, 0, 0};
static char[][] grid;
public static void main(String[] args) {
Scanner sc = new Scanner(System.in);
n = sc.nextInt();
m = sc.nextInt();
grid = new char[n][m];
for(int i = 0; i < n; i++) grid[i] = sc.next().toCharArray();
LinkedList<State> q = new LinkedList<>();
q.add(new State(0, 0, 1));
while(!q.isEmpty()) {
State cur = q.poll();
ans = Math.max(ans, cur.d);
for(int i = 0; i < 4; i++) {
int x = cur.x+dx[i];
int y = cur.y+dy[i];
if(x < 0 || x >= n || y < 0 || y >= m || grid[x][y] == '*') continue;
if (grid[x][y] != grid[cur.x][cur.y]) q.addLast(new State(x, y, cur.d+1));
else q.addFirst(new State(x, y, cur.d));
grid[x][y] = '*';
}
}
System.out.println(ans);
sc.close();
}
public static class State {
int x, y, d;
public State(int x, int y, int d) {
this.x = x;
this.y = y;
this.d = d;
}
}
}
