#include <bits/stdc++.h>
using namespace std;
const int N = 4000;
string snow[N];
int dept[N][N];
int h,w;
int mx[]={1,-1,0,0},my[]={0,0,1,-1};
bool inside(int x,int y){
return (x>=0&&y>=0&&x<h&&y<w&&snow[x][y]!='.');
}
int main(){
//ios::sync_with_stdio(false);
//cin.tie(0);
cin >> h >> w;
for(int i=0;i<h;i++){
cin >> snow[i];
}
deque<pair<int,int>> q;
dept[0][0]=1;
q.push_back({0,0});
int ans=1;
while(!q.empty()){
auto curr = q.front();
q.pop_front();
ans=max(ans,dept[curr.first][curr.second]);
for(int i=0;i<4;i++){
int x=curr.first+mx[i];
int y=curr.second+my[i];
if(inside(x,y)&&dept[x][y]==0){
if(snow[x][y]==snow[curr.first][curr.second]){
dept[x][y]=dept[curr.first][curr.second];
q.push_front({x,y});
}
else{
dept[x][y]=dept[curr.first][curr.second]+1;
q.push_back({x,y});
}
}
}
}
cout << ans << '\n';
}
