#include <bits/stdc++.h>
using namespace std;
#define pii pair<int,int>
#define F first
#define S second
#define pb push_back
#define mp mka
string s[4005];
short int dist[4005][4005];
deque<pair<int, int> > dq;
int h , w;
int dx[4] = { 0 , 1 , 0 , -1};
int dy[4] = {1 , 0 , -1 , 0};
int32_t main(){
ios::sync_with_stdio(false);
cin.tie(0) , cout.tie(0);
cin>>h>>w;
for(int i = 0 ; i < h ; i ++){
cin>>s[i];
for(int j = 0 ; j < w ; j ++){
dist[i][j] = numeric_limits<short>::max();
}
}
dq.push_back(pair<int,int>(0,0));
int ans = 0;
dist[0][0] = 0;
while(!dq.empty()){
pii u = dq.front();
ans = max(ans , dist[u.first][u.second]+1);
dq.pop_front();
for(int i = 0 ; i < 4 ; i++){
int x = u.first + dx[i] , y = u.second + dy[i];
if(x >= 0 && y >= 0 && x < h && y < w){
if(s[x][y] != s[u.first][u.second] && s[x][y] != '.' && dist[x][y] > (dist[u.first][u.second] + 1)){
dist[x][y] = dist[u.first][u.second] + 1;
dq.push_back(pair<int,int>(x,y));
}
else{
if(s[x][y] == s[u.first][u.second] && dist[x][y] > (dist[u.first][u.second])){
dist[x][y] = dist[u.first][u.second];
dq.push_front(pair<int,int>(x,y));
}
}
}
}
}
cout<<ans<<"\n";
}
