#include <bits/stdc++.h>
using namespace std;
#define ff first
#define ss second
#define pb push_back
typedef long long ll;
typedef pair<int,int> pii;
const int S = 4000;
char meadow[S][S];
int dist[S][S];
bool vis[S][S];
const int INF = 1e8;
void reset(){
for(int i = 0; i < S; i++){
for(int j = 0; j < S; j++){
dist[i][j] = INF;
}
}
}
int solve(int h, int w){
reset();
int ans = 0;
pii start = {0,0};
deque<pii> dq;
dq.push_back(start);
dist[0][0] = 0;
while(dq.size()){
auto [a, b] = dq.front(); dq.pop_front();
if(vis[a][b]) continue;
vis[a][b] = true;
char animal = meadow[a][b];
// obtener vecinos
vector<pii> vecinos;
if (a > 0){
if(!vis[a-1][b]){
pii up = {a-1, b};
char animal_up = meadow[up.ff][up.ss];
if(animal_up != '.'){
vecinos.pb(up);
}
}
}
if(a < h-1){
if(!vis[a+1][b]){
pii down = {a+1, b};
char animal_down = meadow[down.ff][down.ss];
if(animal_down != '.'){
vecinos.pb(down);
}
}
}
if(b > 0){
if(!vis[a][b-1]){
pii left = {a, b-1};
char animal_left = meadow[left.ff][left.ss];
if(animal_left != '.'){
vecinos.pb(left);
}
}
}
if(b < w-1){
if(!vis[a][b+1]){
pii right = {a, b+1};
char animal_right = meadow[right.ff][right.ss];
if(animal_right != '.'){
vecinos.pb(right);
}
}
}
// iterar por vecinos
for(auto [x,y]: vecinos){
int d = 0;
if(meadow[x][y] != animal){
d = 1;
}
// if (dist[curr_node] + d > dist[to]) continue;
if(dist[a][b] + d > dist[x][y]) continue;
dist[x][y] = dist[a][b] + d;
ans = max(ans, dist[x][y]);
if(d == 1){
dq.push_back({x,y});
}
else if(d == 0){
dq.push_front({x,y});
}
}
}
return ans;
}
int main() {
ios::sync_with_stdio(0);
cin.tie(0);
int h, w; cin >> h >> w;
for(int i = 0; i < h; i++){
for(int j = 0; j < w; j++){
char x; cin >> x;
meadow[i][j] = x;
}
}
cout << solve(h,w)+1;
}
