#include <bits/stdc++.h>
#define int int64_t //be careful about this
using namespace std;
#define vt vector
#define ar array
#define pr pair
#define f first
#define s second
#define pb push_back
#define eb emplace_back
#define fr(i,a,b) for(int i = a; i < b; ++i)
#define rf(i,a,b) for(int i = a-1; i >= b; --i)
#define all(x) x.begin(),x.end()
#define mem(a,b) memset(a,b,sizeof(a))
using VI = vector<int>;
using VVI = vector<vector<int>>;
namespace IN{
template<class T> void re(vector<T> &A);
template<class S,class T> void re(pair<S,T> &A);
template<class T,size_t N> void re(array<T,N> &A);
template<class T> void re(T& x){
cin >> x;}
template<class H, class... T> void re(H& h, T&... t){
re(h); re(t...);}
template<class T> void re(vector<T> &A){
for(auto& x : A) re(x);}
template<class S,class T> void re(pair<S,T> &A){
re(A.first); re(A.second);}
template<class T,size_t N> void re(array<T,N> &A){
for(int i = 0; i < N; ++i) re(A[i]);}
}
namespace OUT{
template<class T>
void __p(const T& a){ cout<<a; }
template<class T, class F>
void __p(const pair<T, F>& a){ cout<<"{"; __p(a.first); cout<<","; __p(a.second); cout<<"}\n"; }
template<class T, size_t N>
void __p(const array<T,N>& a){ cout<<"{"; for(int i=0;i<N;++i)__p(a[i]),cout<<",}\n"[i+1==N]; }
template<class T>
void __p(const vector<T>& a){
cout<<"{";for(auto it=a.begin();it<a.end();it++)__p(*it),cout<<",}\n"[it+1==a.end()]; }
template<class T, class ...Arg>
void __p(T a1, Arg ...a){__p(a1); __p(a...); }
template<class Arg1>
void __f(const char *s, Arg1 &&arg1){ cout<<s<<" : "; __p(arg1); cout<<endl; }
template<class Arg1, class ... Args>
void __f(const char *ss, Arg1 &&arg1, Args &&... args){
int b=0,i=0; do{ if(ss[i]=='(') b++; if(ss[i]==')') b--; i++;}while(!(ss[i]==','&&b==0));
const char *comma=ss+i; cout.write(ss,comma-ss)<<" : ";__p(arg1);cout<<" | ";__f(comma+1,args...);}
#define trace(...) cout<<"Line:"<<__LINE__<<" ", __f(#__VA_ARGS__, __VA_ARGS__)
}
namespace FUN{
void IO(string s = ""){
ios_base::sync_with_stdio(NULL);
cin.tie(nullptr);
cout.precision(20);
cout << fixed;
if(!s.empty()){
freopen((s+".in").c_str(),"r",stdin);
freopen((s+".out").c_str(),"w",stdout);
}
}
const auto start_time = chrono::high_resolution_clock::now();
void output_run_time(){
// will work for ac,cc&&cf.
#ifndef ONLINE_JUDGE
auto end_time = chrono::high_resolution_clock::now();
chrono::duration<double> diff = end_time-start_time;
cout << "\n\n\nTime Taken : " << diff.count();
#endif
}
template<class T> bool ckmin(T& a, const T& b){
return b < a ? a = b, true : false; }
template<class T> bool ckmax(T& a, const T& b){
return a < b ? a = b, true : false; }
mt19937_64 rng(chrono::steady_clock::now().time_since_epoch().count());
int my_rand(int L, int R){
return uniform_int_distribution<int>(L,R)(rng); }
template<class T> int sz(const T& x){
return int(x.size()); }
template<class T> int lb(const vector<T>& vec,const T& val){
return int(lower_bound(vec.begin(), vec.end(),val) - vec.begin()); }
template<class T> int ub(const vector<T>& vec,const T& val){
return int(upper_bound(vec.begin(), vec.end(),val) - vec.begin()); }
constexpr int dx[4] = {1,0,-1,0};
constexpr int dy[4] = {0,1,0,-1};
constexpr long long INFLL1 = 1e16, INFLL2 = 9e18;
constexpr int INF = 2e9;
}
using namespace IN;
using namespace OUT;
using namespace FUN;
signed main(){
IO();
int n,m;
re(n,m);
vector<string> a(n);
re(a);
if(a[0][0] == '.'){
cout << 0;
return 0;
}
VVI dis(n,VI (m,INF));
bool vis[n][m];
mem(vis,0);
int ans = 1;
deque<pair<int,int>> q;
q.push_back({0,0});
vis[0][0] = 1;
dis[0][0] = 1;
while(!q.empty()){
auto [i,j] = q.front(); q.pop_front();
fr(k,0,4){
int ni = i + dx[k], nj = j + dy[k];
if(ni >= 0 && ni < n && nj >= 0 && nj < m && a[ni][nj] != '.' && !vis[ni][nj]){
if(a[ni][nj] == a[i][j]){
dis[ni][nj] = dis[i][j];
vis[ni][nj] = 1;
q.push_front({ni,nj});
}else{
dis[ni][nj] = dis[i][j] + 1;
ckmax(ans,dis[ni][nj]);
vis[ni][nj] = 1;
q.push_back({ni,nj});
}
}
}
}
cout << ans;
output_run_time();
return 0;
}
