#include <bits/stdc++.h>
using namespace std;
typedef pair<long long, long long> pii;
typedef long long ll;
typedef long double ld;
const long long MAXLOG = 23;
const long long MAXN = 4*1e3+3; // use com cuidado
const long long MOD = 998244353;
const long long inf = 1e9 + 10;
const long long TWO_MOD_INV = 500000004;
#define pb push_back
#define mp make_pair
#define f first
#define s second
#define KAMEKAMEHA ios_base::sync_with_stdio(0); ios::sync_with_stdio(0); cin.tie(0); cout.tie(0);
#define sz(x) (int)x.size()
vector<ll> dist(MAXN, inf);
vector<pii> grafo[MAXN*MAXN];
void bfs() {
deque<ll> pq;
dist[1]=0;
pq.push_back(1);
while(!pq.empty()) {
ll v=pq.front();
pq.pop_front();
for(auto i : grafo[v]) {
if(dist[i.f]>dist[v] + i.s) {
dist[i.f]=dist[v] + i.s;
if(i.s) {
pq.push_back(i.f);
} else {
pq.push_front(i.f);
}
}
}
}
}
int main() {
KAMEKAMEHA
#ifdef FRAGA
freopen("output.out", "w", stdout);
freopen("err.er", "w", stderr);
#endif
#ifndef FRAGA
//freopen("cbarn2.in", "r", stdin);
//freopen("cbarn2.out", "w", stdout);
#endif
ll h, w;
cin>>h>>w;
char mat[MAXN][MAXN];
for(ll i=0;i<=h+1;i++) {
for(ll j=0;j<=w+1;j++) {
mat[i][j]='.';
}
}
for(ll i=1;i<=h;i++) {
for(ll j=1;j<=w;j++) {
cin>>mat[i][j];
}
}
for(ll i=1;i<=h;i++) {
for(ll j=1;j<=w;j++) {
if(mat[i][j]=='.') continue;
ll atu=(i-1)*w+j;
if(mat[i-1][j]!='.') {
if(mat[i+1][j]==mat[i][j]) {
grafo[atu].pb(mp((i-2)*w+j, 0));
} else {
grafo[atu].pb(mp((i-2)*w+j, 1));
}
}
if(mat[i+1][j]!='.') {
if(mat[i+1][j]==mat[i][j]) {
grafo[atu].pb(mp((i)*w+j, 0));
} else {
grafo[atu].pb(mp((i)*w+j, 1));
}
}
if(mat[i][j-1]!='.') {
if(mat[i][j-1]==mat[i][j]) {
grafo[atu].pb(mp((i-1)*w+j-1, 0));
} else {
grafo[atu].pb(mp((i-1)*w+j-1, 1));
}
}
if(mat[i][j+1]!='.') {
if(mat[i][j+1]==mat[i][j]) {
grafo[atu].pb(mp((i-1)*w+j+1, 0));
} else {
grafo[atu].pb(mp((i-1)*w+j+1, 1));
}
}
}
}
bfs();
ll mt=0;
for(ll i=1;i<=h*w;i++) {
if(dist[i]!=inf)
mt=max(mt, dist[i]);
}
cout<<mt+1<<endl;
//indices conflitantes
}
