#include <iostream>
#include <vector>
#include <map>
#include <algorithm>
#include <string>
#include <queue>
#include <stack>
#define int long long // vse ti je long long
#define vi vector<int>
#define vpii vector<pair<int,int>>
#define oopt cin.tie(0);cout.tie(0);ios_base::sync_with_stdio(false);
#define forn(i,n) for(int i = 0; i<n; i++)
#define all(x) (x).begin(), (x).end()
#define vvi vector<vi>
using namespace std;
int h,w;
queue<pair<int,int>> q;
int x, y;
int ans = 0;
vector<vector<bool>> visited;
vector<vector<char>> tabela(h,vector<char>(w));
vector<vector<int>> globina(h,vector<int>(w,1));
bool valid(int y, int x){
if(x<0 || x>=w || y<0 || y>=h || visited[y][x]) return 0;
return 1;
}
void Flood(int y2, int x2);
void Sirjenje(int y,int x){
Flood(y+1,x);
Flood(y-1,x);
Flood(y,x+1);
Flood(y,x-1);
}
void Flood(int y2, int x2){
if(valid(y2,x2)){
visited[y2][x2] = true;
if(tabela[y2][x2] == '.') return;
else {
if(tabela[y2][x2] == tabela[y][x]){ //naš je, takoj naprej
globina[y2][x2] = globina[y][x];
Sirjenje(y2,x2);
}else{
globina[y2][x2] = globina[y][x]+1;
ans = max(ans,globina[y2][x2]);
q.push({y2,x2});
}
}
}
}
signed main() {
cin >> h>>w;
visited.resize(h,vector<bool>(w,false));
tabela.resize(h,vector<char>(w));
globina.resize(h,vector<int>(w,0));
forn(i,h){
forn(j,w){
cin >> tabela[i][j];
}
}
char prvi = tabela[0][0];
globina[0][0] = 1;
q.push({0,0});
visited[0][0] = true;
while(!q.empty()){
pair<int,int> zdaj = q.front(); q.pop();
y = zdaj.first;
x = zdaj.second;
//pogledamo sosede
Sirjenje(y,x);
}
/*
forn(i,h){
forn(j,w){
cout << globina[i][j];
}
cout << "\n";
}*/
cout << ans <<"\n";
return 0;
}
