#include <iostream>
#include <vector>
#include <algorithm>
#include <map>
#include <fstream>
#include <string>
#include <bits/stdc++.h>
#include <deque>
#include <numeric>
using namespace std;
#define FOR(i,L,R) for (int i = L; i < R; i++)
#define FOR_STEP(i,L,R, STEP) for (int i = L; i < R; i+= STEP)
struct coord {
int x;
int y;
};
int main(){
int H, W;
cin >> H >> W;
char array[H][W];
int d[H][W];
// use '.' as visited
FOR(i, 0, H) {
FOR(j, 0, W) {
char x; cin >> x;
array[i][j] = x;
d[i][j] = INT_MAX;
}
}
int left[] = {-1, 1, 0, 0};
int right[] = {0, 0, -1, 1};
deque<coord> bfs_queue;
bfs_queue.push_front({0, 0});
d[0][0] = 0;
while (!bfs_queue.empty()) {
coord topCoord = bfs_queue.front();
bfs_queue.pop_front();
FOR (i, 0, 4) {
int nx = topCoord.x + left[i];
int ny = topCoord.y + right[i];
if (nx >=0 && nx < H && ny <W && ny >= 0) {
if (array[nx][ny] != '.') {
if (array[nx][ny] == array[topCoord.x][topCoord.y] && d[topCoord.x][topCoord.y] < d[nx][ny]) {
bfs_queue.push_front({nx, ny});
d[nx][ny] = d[topCoord.x][topCoord.y];
} else if (array[nx][ny] != array[topCoord.x][topCoord.y] && d[topCoord.x][topCoord.y] + 1 < d[nx][ny]){
bfs_queue.push_back({nx, ny});
d[nx][ny] = d[topCoord.x][topCoord.y] + 1;
}
}
}
}
array[topCoord.x][topCoord.y] = '.';
}
int maxDepth = 0;
FOR (i, 0, H) {
FOR (j, 0, W) {
if (d[i][j] != INT_MAX && d[i][j] > maxDepth) {
maxDepth = d[i][j];
}
}
}
cout << maxDepth + 1;
}
