#pragma GCC optimize("O3")
#include <bits/stdc++.h>
using namespace std;
#include <ext/pb_ds/assoc_container.hpp>
#include <ext/pb_ds/tree_policy.hpp>
using namespace __gnu_pbds;
template <typename T>
using ordered_set = tree<T, null_type, less_equal<T>, rb_tree_tag, tree_order_statistics_node_update>;
#include <iostream>
#include <stack>
#include <fstream>
#include <cstdio>
#include <numeric>
#include <time.h>
#include <sys/timeb.h>
#define double long double
#define vi vector<int>
#define pb push_back
#define ll long long
#define ld long double
#define fi first
#define se second
#define pii pair<int,int>
#define sz(a) (int)a.size()
#define revall(a) a.rbegin(), a.rend()
#define all(a) a.begin(),a.end()
#define int_max INT64_MAX/2
#define int_min INT64_MIN/2
#define multierase (a, x) a.erase(a.find(x))
#define pq priority_queue
#define pqr priority_queue<int, vector<int>, greater<int>>
#define contains (a, x) a.find(x)!=a.end()
#define MOD 1000000007
#define SMOD 998244353
#define ODDMOD 100000000
mt19937_64 rng(chrono::steady_clock::now().time_since_epoch().count());
void setIO(string name = ""){
ios_base::sync_with_stdio(0);
cin.tie(0);
if (!name.empty()) {
freopen((name + ".in").c_str(), "r", stdin);
freopen((name + ".out").c_str(), "w", stdout);
}
}
void read(vi& arr, int n) {
for(int i=0;i<n;i++){
int a;
cin>>a;
arr.pb(a);
}
}
void print(pii p) {
cout<<"[ "<<p.first<<" "<<p.second<<" ]"<<endl;
}
void print(vi arr) {
for(int i : arr) {
if(i==int_max)
cout<<"i ";
else if(i==int_min)
cout<<"-i ";
else
cout<<i<<" ";
}
cout<<endl;
}
int ceil_div(int a, int b) {
if(a%b==0) {
return a/b;
}else {
return (a/b)+1;
}
}
int h,w;
vector<string> grid;
vector<vi> rep;
void ff(int x, int y, int crep, char gval) {
if(x<0||y<0||x>=w||y>=h) return;
if(grid[y][x]!=gval) return;
if(rep[y][x]!=0) return;
rep[y][x]=crep;
ff(x-1, y, crep,gval);
ff(x+1, y, crep,gval);
ff(x,y+1,crep,gval);
ff(x,y-1,crep,gval);
}
void solve() {
cin>>h>>w;
grid.clear();
for(int i=0;i<h;i++) {
string s;
cin>>s;
grid.pb(s);
}
rep=vector<vi>(h, vi(w, 0));
int crep=1;
for(int i=0;i<h;i++) {
for(int j=0;j<w;j++) {
if(rep[i][j]==0&&grid[i][j]!='.') {
ff(j,i,crep, grid[i][j]);
crep++;
}
}
}
vector<set<int>> adj;
adj.resize(crep);
for(int i=0;i<h;i++) {
for(int j=0;j<w;j++) {
if(i!=(h-1)&&rep[i][j]!=0&&rep[i+1][j]!=0) {
adj[rep[i][j]].insert(rep[i+1][j]);
adj[rep[i+1][j]].insert(rep[i][j]);
}
if(j!=(w-1)&&rep[i][j]!=0&&rep[i][j+1]!=0) {
adj[rep[i][j]].insert(rep[i][j+1]);
adj[rep[i][j+1]].insert(rep[i][j]);
}
}
}
vi dist (crep, int_max);
queue<int> Q;
Q.push(1);
dist[1]=0;
while(!Q.empty()) {
int c=Q.front();
Q.pop();
for(int i:adj[c]) {
if(dist[i]>dist[c]+1) {
dist[i]=dist[c]+1;
Q.push(i);
}
}
}
int res=0;
for(int i=1;i<crep;i++) {
res=max(res, dist[i]);
}
cout<<res+1<<endl;
}
signed main() {
cin.tie(0)->sync_with_stdio(0);
// int x;
// cin>>x;
// while(x>0) {
solve();
// x--;
// }
}
