#include<bits/stdc++.h>
#define ll int
#define F first
#define S second
#define pb push_back
#define mpr make_pair
const ll N=5e5 + 10 , mod=1e9 + 7;
using namespace std;
ll n,a,m;
ll t[N];
string ch[4100];
ll c=0;
ll com[4100][4100];
bool vis[4100][4100];
ll x,y;
void ff(ll i,ll j){
if(i<0 || i>=n || j<0 || j>=m || ch[x][y]!=ch[i][j] || vis[i][j])
return;
//cout<<i<<" "<<j<<" "<<x<<" "<<y<<"\n";
vis[i][j]=1;
com[i][j]=c;
ff(i-1,j);
ff(i+1,j);
ff(i,j+1);
ff(i,j-1);
return ;
}
int main(){
// ios_base::sync_with_stdio (0); cin.tie(0),cout.tie(0);
// freopen("odometer.in","r",stdin);
// freopen("odometer.out","w",stdout);
ll T=1;
// cin>>T;
while(T--){
cin>>n>>m;
for(ll i=0;i<n;i++){
cin>>ch[i];
}
for(ll i=0;i<n;i++){
for(ll j=0;j<m;j++){
if(!vis[i][j]){
c++;
x=i;y=j;
ff(i,j);
}
//cout<<com[i][j];
}
// cout<<"\n";
}
// cout<<"jsldkj";
vector<vector<ll>>adj(c+1);
for(ll i=0;i<n;i++){
for(ll j=0;j<m;j++){
if(ch[i][j]!='.') {
if(i+1<n){
if(ch[i][j]!=ch[i+1][j] && ch[i+1][j]!='.'){
adj[com[i][j]].pb(com[i+1][j]);
adj[com[i+1][j]].pb(com[i][j]);
}
}
if(j+1<m){
if(ch[i][j]!=ch[i][j+1] && ch[i][j+1]!='.'){
adj[com[i][j]].pb(com[i][j+1]);
adj[com[i][j+1]].pb(com[i][j]);
}
}
}
}
}
vector<ll>d(c+1,1e9);
d[1]=0;
queue<ll>q;
q.push(1);
ll res=0;
while(!q.empty()){
ll node=q.front();
q.pop();
for(ll x:adj[node]){
if(d[x]>d[node]+1){
d[x]=d[node]+1;
q.push(x);
res=max(res,d[x]);
}
}
}
cout<<res+1<<"\n";
}
return 0;
}
/*
1 5 6 5
*/
