#include <bits/stdc++.h>
using namespace std;
#define ll long long
#define ull unsigned long long
#define pb(e) push_back(e)
#define sv(a) sort(a.begin(),a.end())
#define sa(a,n) sort(a,a+n)
#define mp(a,b) make_pair(a,b)
#define vf first
#define vs second
#define ar array
#define all(x) x.begin(),x.end()
const int inf = 0x3f3f3f3f;
const int mod = 1000000007;
const double PI=3.14159265358979323846264338327950288419716939937510582097494459230;
mt19937_64 RNG(chrono::steady_clock::now().time_since_epoch().count());
bool remender(ll a , ll b){return a%b;}
//freopen("problemname.in", "r", stdin);
//freopen("problemname.out", "w", stdout);
int n , m;
int convert(int r , int w){
return r*m+w;
}
pair<int,int> back(int x){
return mp(x/m,x%m);
}
struct ufds {
vector<int> siz,p;
void init(int nn){
siz.resize(nn + 1);
p.resize(nn + 1);
for(int i = 0; i <= nn; i++){
siz[i] = 1;
p[i] = i;
}
}
int get(int x){
return p[x] = (p[x] == x ? x : get(p[x]));
}
void unio(int x , int y){
x = get(x);
y = get(y);
if(x == y)return;
if(siz[y] > siz[x])swap(x,y);
p[y] = x;
siz[x] += siz[y];
}
};
int dx[4] = {1,0}, dy[4] = {0,1};
void solve(){
cin >> n;
cin >> m;
char arr[n][m];
for(int i = 0; i < n; i++){
for(int j = 0; j < m; j++)cin >> arr[i][j];
}
ufds dsu;
dsu.init(n*m+1);
for(int i = 0; i < n; i++){
for(int j = 0; j < m; j++){
if(arr[i][j] == '.')continue;
for(int k = 0; k < 2; k++){
int ni = i + dx[k] , nj = j + dy[k];
if(ni < n && nj < m && ni >= 0 && nj >= 0 && arr[i][j] == arr[ni][nj]){
dsu.unio(convert(i,j),convert(ni,nj));
}
}
}
}
vector<int> adj[n*m];
for(int i = 0; i < n; i++){
for(int j = 0; j < m; j++){
if(arr[i][j] == '.')continue;
for(int k = 0; k < 2; k++){
int ni = i + dx[k] , nj = j + dy[k];
if(ni < n && ni >= 0 && nj < m && nj >= 0 && arr[ni][nj]!='.'){
int a = convert(ni,nj);
int b = convert(i,j);
a = dsu.get(a);
b = dsu.get(b);
if(a==b)continue;
adj[a].pb(b);
adj[b].pb(a);
}
}
}
}
int dis[n*m];
queue<int> q;
memset(dis,-1,sizeof dis);
dis[dsu.get(0)] = 1;
q.push(dsu.get(0));
int ans = 1;
while(q.size()){
int node = q.front();
q.pop();
for(int i : adj[node]){
int par = dsu.get(i);
if(dis[par] == -1){
dis[par] = dis[node] + 1;
ans = dis[par];
q.push(par);
}
}
}
cout << ans << '\n';
}
int main(){
ios_base::sync_with_stdio(false);
cin.tie(NULL);
// int t;cin>>t;
// while(t--){
solve();
//}
return 0;
}
