#include <bits/stdc++.h>
using namespace std;
#define int long long
#define OYY 1e11
#define mod 100000000
#define faster ios_base::sync_with_stdio(false);cin.tie(NULL);cout.tie(NULL);
#define mid (start+end)/2
char dizi[4005][4005];
int cev=0,x[4]={1,-1,0,0},y[4]={0,0,1,-1},dep[4005][4005],n,m;
inline int bfs(){
deque <pair<int,int>> de;
de.push_back({0,0});
dep[0][0]=1;
while(de.size()){
int x1=de.front().first;
int y1=de.front().second;
de.pop_front();
cev=max(cev,dep[x1][y1]);
for(int i=0;i<4;i++){
int yx=x1+x[i],yy=y1+y[i];
if(yx<0 || yx>=n || yy<0 || yy>=m)continue;
if(dizi[yx][yy]=='.')continue;
if(dep[yx][yy]!=0)continue;
if(dizi[yx][yy]==dizi[x1][y1]){
dep[yx][yy]=dep[x1][y1];
de.push_front({yx,yy});
}else{
dep[yx][yy]=dep[x1][y1]+1;
de.push_back({yx,yy});
}
}
}
return cev;
}
int32_t main(){
faster
cin>>n>>m;
string deg;
for(int i=0;i<n;i++){
cin>>deg;
for(int j=0;j<m;j++){
dizi[i][j]=deg[j];
}
}
cout<<bfs()<<'\n';
return 0;
}
