/**
* If you live in imaginary world when your imaginary situation encounter in
* real situation you can't enjoiy it because you have to do pending work.
* {This pending work appeared because you wasted that time for your useless
* imagianry thinking .}
*/
#include<bits/stdc++.h>
using namespace std;
//#define int int64_t
#define all(x) x.begin(),x.end()
#define all1(x) x.rbegin(),x.rend()
#define sz(x) (int)(x.size())
const int N=4e5+5,mod=1e9+7;
void solve(){
int n,m;
cin>>n>>m;
vector<string> z(n);
for (string &it:z){cin>>it;}
int ans=0;
deque<pair<int,int>> q;
vector<vector<int>> dis(n,vector<int>(n));
dis[0][0]=1;
q.emplace_back(0,0);
vector<int> dx{1,-1,0,0},dy{0,0,1,-1};
while(!q.empty()){
pair<int,int> u=q.front();
q.pop_front();
ans=max(ans,dis[u.first][u.second]);
for (int i=0;i<4;i++){
int x=u.first+dx[i],y=u.second+dy[i];
if (min(x,y)>=0 && x<n && y<m && z[x][y]!='.' && dis[x][y]==0){
if (z[u.first][u.second]==z[x][y]){
q.emplace_front(x,y);
dis[x][y]=dis[u.first][u.second];
}
else{
q.emplace_back(x,y);
dis[x][y]=dis[u.first][u.second]+1;
}
}
}
}
cout<<ans;
}
int32_t main(){
ios::sync_with_stdio(false);cin.tie(nullptr);cout.tie(nullptr);
int tq=1;
//cin>>tq;
for (;tq;tq--){solve();}
}
//is a bruteforce possible?
//think greedier, make more assumptions
// if we you find solution using loop to decrease complexity use bs
//stuck for more than 5 minutes? move on
