#include <bits/stdc++.h>
using namespace std;
const int MAX_H = 4000;
const int MAX_W = 4000;
vector <string> meadow(MAX_H);
int dis[MAX_H][MAX_W];
bool visited[MAX_H][MAX_W];
int dx[] = {-1, 1, 0, 0};
int dy[] = {0, 0, -1, 1};
bool diff_animal(int x, int y, int diffx, int diffy){
if (meadow[x][y] != meadow[x + diffx][y + diffy])
return true;
return false;
}
bool valid_sq(int x, int y, int h, int w){
if (x >= 0 && x < h && y >= 0 && y < w && meadow[x][y] != '.')
return true;
return false;
}
int main()
{
int h, w;
cin >> h >> w;
for (int i = 0; i < h; i++)
cin >> meadow[i];
deque <pair <int, int>> q;
memset(dis, -1, sizeof(dis));
int ans = 0;
dis[0][0] = 0;
q.push_back({0, 0});
while (!q.empty()){
int x = q.front().first, y = q.front().second;
q.pop_front();
ans = max(ans, dis[x][y]);
for (int i = 0; i < 4; i++){
int curr_x = x + dx[i], curr_y = y + dy[i];
if (valid_sq(curr_x, curr_y, h, w) && dis[curr_x][curr_y] == -1){
int d = diff_animal(x, y, dx[i], dy[i]);
dis[curr_x][curr_y] = dis[x][y] + d;
if (d == 0)
q.push_front({curr_x, curr_y});
else
q.push_back({curr_x, curr_y});
}
}
}
cout << ans + 1 << '\n';
}
