#include <iostream>
#include <queue>
using namespace std;
int n,m;
const int MAXN = 4010;
int dx[5] = {1,0,-1,0};
int dy[5] = {0,1,0,-1};
string arr[MAXN];
int dp[MAXN][MAXN];
int ans;
bool check(int x,int y){
if(x>0 && x<=n && y>0 && y<=m && arr[x][y]!='.'){
return true;
}
return false;
}
deque<pair<int,int>> q1;
int main(){
cin>>n>>m;
for(int i=1;i<=n;i++){
cin>>arr[i];
arr[i] = '.'+arr[i];
//cout<<arr[i]<<endl;
}
dp[1][1] = 1;
q1.push_front(make_pair(1,1));
while(!q1.empty()){
auto curr = q1.front();
q1.pop_front();
ans = max(ans,dp[curr.first][curr.second]);
for(int i=0;i<4;i++){
int x = curr.first+dx[i];
int y = curr.second+dy[i];
if(check(x,y) && dp[x][y]==0){
if(arr[x][y] == arr[curr.first][curr.second]){
q1.push_front(make_pair(x,y));
dp[x][y] = dp[curr.first][curr.second];
}else{
q1.push_back(make_pair(x,y));
dp[x][y] = dp[curr.first][curr.second]+1;
}
}
}
}
cout<<ans<<endl;
}
