#include <bits/stdc++.h>
using namespace std;
using ll=long long;
#define endl "\n"
///freopen("input.txt", "r", stdin);
///freopen("output.txt", "w", stdout);
void solve(){
int n,m;
cin>>n>>m;
vector<string>mat(n);
for(int i=0;i<n;i++){
cin>>mat[i];
}
int dx[]={-1,0,0,1};
int dy[]={0,-1,1,0};
vector<vector<int>>dubina(n,vector<int>(m));
deque<pair<int,int>>dq;
dq.push_back({0,0});
dubina[0][0]=1;
int ans=1;
while(!dq.empty()){
auto v=dq.front();
dq.pop_front();
ans=max(ans,dubina[v.first][v.second]);
for(int i=0;i<4;i++){
int x=v.first+dx[i];
int y=v.second+dy[i];
if(0<=x&&x<n&&0<=y&&y<m&&mat[x][y]!='.'&&dubina[x][y]==0){
dubina[x][y]=dubina[v.first][v.second];
if(mat[x][y]==mat[v.first][v.second]){
dq.push_front({x,y});
}
else{
dq.push_back({x,y});
dubina[x][y]++;
}
}
}
}
cout<<ans<<endl;
}
int main(){
ios_base::sync_with_stdio(false);cin.tie(0);
int t=1;///cin>>t;
while(t--)solve();
return 0;
}
