//UPDATERA ARRAY STORLEKEN!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!
#include <bits/stdc++.h>
using namespace std;
typedef long long ll;
const ll INF=1e15;
const ll MAXN=4006;//UPDATERA ARRAY STORLEKEN!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!
ll n,ans,m,dist[MAXN*MAXN];
bool already[MAXN*MAXN];
char lst[MAXN*MAXN];
int Link[MAXN*MAXN],cnt;
struct node{
int end,next,w;
}Edge[2*MAXN*MAXN];
void insert(int x,int y,int z){
int temp=Link[x];
cnt++;
Link[x]=cnt;
Edge[cnt].next=temp;
Edge[cnt].end=y;
Edge[cnt].w=z;
}
int main(){
ios_base::sync_with_stdio(false);
cin.tie(NULL);
cin>>n>>m;
for(int i=1;i<=n*m;i++){
cin>>lst[i];
dist[i]=INF;
}
for(int i=1;i<=n*m;i++){
if(i%m!=1&&lst[i]!='.'&&lst[i-1]!='.'){
if(lst[i]==lst[i-1]){//need not a dot
insert(i,i-1,0);
}else insert(i,i-1,1);
}
if(i%m!=0&&lst[i]!='.'&&lst[i+1]!='.'){
if(lst[i]==lst[i+1]){
insert(i,i+1,0);
}else insert(i,i+1,1);
}
if(i>m&&lst[i]!='.'&&lst[i-m]!='.'){
if(lst[i]==lst[i-m]){
insert(i,i-m,0);
}else insert(i,i-m,1);
}
if(i<=n*m-m&&lst[i]!='.'&&lst[i+m]!='.'){
if(lst[i]==lst[i+m]){
insert(i,i+m,0);
}else insert(i,i+m,1);
}
}
deque<ll> Q;
Q.push_back(1);
dist[1]=0;
while(!Q.empty()){
ll a=Q.front();
Q.pop_front();
if(already[a]) continue;
already[a]=1;
for(int i=Link[a];i;i=Edge[i].next){
if(dist[Edge[i].end]>dist[a]+Edge[i].w){
dist[Edge[i].end]=dist[a]+Edge[i].w;
if(Edge[i].w==0){
Q.push_front(Edge[i].end);
}else Q.push_back(Edge[i].end);
}
}
}
for(int i=1;i<=n*m;i++){
if(lst[i]!='.') ans=max(ans,dist[i]);
}
cout<<ans+1<<'\n';
}
