#include <bits/stdc++.h>
#define endl "\n"
#define ll long long
#define fi first
#define se second
#define all(x) x.begin(),x.end()
#define gett(tup,ind) get<ind>(tup)
#define print(x) for (auto i:x){cout<<i<<" ";}cout<<endl;
using namespace std;
void solve(){
int h,w;cin>>h>>w;
vector <string> arr(h);
for (int i=0;i<h;i++){
cin>>arr[i];
}
vector <vector<int>> dis(h,vector <int> (w,-1));
deque <tuple<int,int,int>> dq;dq.emplace_back(0,0,1);
while (dq.size()){
auto [a,b,c]=dq.front();dq.pop_front();
if (dis[a][b]!=-1)continue;
dis[a][b]=c;
if (a+1<h && arr[a+1][b]!='.'){if (arr[a][b]==arr[a+1][b]){dq.emplace_front(a+1,b,c);}else{dq.emplace_back(a+1,b,c+1);}}
if (b+1<w && arr[a][b+1]!='.'){if (arr[a][b]==arr[a][b+1]){dq.emplace_front(a,b+1,c);}else{dq.emplace_back(a,b+1,c+1);}}
if (a>0 && arr[a-1][b]!='.'){if (arr[a][b]==arr[a-1][b]){dq.emplace_front(a-1,b,c);}else{dq.emplace_back(a-1,b,c+1);}}
if (b>0 && arr[a][b-1]!='.'){if (arr[a][b]==arr[a][b-1]){dq.emplace_front(a,b-1,c);}else{dq.emplace_back(a,b-1,c+1);}}
}
int ans=0;
for (auto i:dis){
ans=max(ans,*max_element(all(i)));
}
cout<<ans<<endl;
return;
}
int main(){
ios_base::sync_with_stdio(false);
cin.tie(NULL);
int no_test=1;
//cin>>no_test;
while (no_test--){solve();}
return 0;
}
