/*
* Se me ocurre ir desde el principio hasta el final marcando el camino que contenga la misma especie
* y luego si es distinto aumentar la distancia a 1
*/
#include <bits/stdc++.h>
using namespace std;
#define forsn(i,s,n) for(int i=s; i<n; ++i)
#define forn(i,n) forsn(i,0,n)
#define pb push_back
#define snd second
#define fst first
#define all(x) x.begin(), x.end()
#define imp(x) for(auto __:x)cout<<__<<" "; cout<<endl;
#define sz(c) int((c).size())
using ll = long long;
const int inf=1e9;
struct Node{
int x,y;
char z;
};
int di[4]={1, -1, 0, 0};
int dj[4]={0, 0, 1, -1};
int main(){
ios_base::sync_with_stdio(false);
cin.tie(nullptr);
int n,m;cin>>n>>m;
vector<string> adj(n);
forn(i,n){
cin>>adj[i];
}
vector<vector<int>> dist(n, vector<int>(m, inf));
deque<Node> q;
q.pb({0, 0, adj[0][0]});
dist[0][0]=0;
auto safe=[&](int i, int j){
return (i<n&&j<m&&i>=0&&j>=0&&adj[i][j]!='.');
};
while(!q.empty()){
auto [i,j,c]=q.front();
q.pop_front();
forn(k,4){
int ni=i+di[k], nj=j+dj[k];
if(safe(ni, nj)){
int w=(adj[ni][nj]!=c);
if(dist[i][j]+w<dist[ni][nj]){
dist[ni][nj]=dist[i][j]+w;
if(w==0){
q.push_front({ni,nj,adj[ni][nj]});
}else{
q.pb({ni,nj,adj[ni][nj]});
}
}
}
}
}
int ans=0;
forn(i,n){
forn(j,m){
if(dist[i][j]==inf)continue;
ans=max(ans, dist[i][j]);
}
cout<<endl;
}
cout<<ans+1<<endl;
}
