#include <bits/stdc++.h>
using namespace std;
struct s{
int x, y, d;
};
int dx[] = {0, 0, -1, 1};
int dy[] = {1, -1, 0, 0};
int H, W;
string m[4000];
bool vis[4000][4000];
int32_t main(){
ios::sync_with_stdio(false);
cin.tie(NULL);
cin >> H >> W;
for(int i = 0; i < H; i++){
cin >> m[i];
}
deque<s> q;
q.push_back({0, 0, 1});
int ans = 0;
while(!q.empty()){
s cur = q.front();
q.pop_front();
int x = cur.x, y = cur.y, d = cur.d;
if(vis[x][y]) continue;
vis[x][y] = true;
ans = max(ans, d);
for(int i = 0; i < 4; i++){
int nx = x + dx[i], ny = y + dy[i];
if(nx < 0 || ny < 0 || nx >= H || ny >= W || m[nx][ny] == '.') continue;
if(m[x][y] != m[nx][ny]){
q.push_back({nx, ny, d+1});
}else{
q.push_front({nx, ny, d});
}
}
}
cout << ans << endl;
}
