#include <iostream>
#include <fstream>
#include <algorithm>
#include <vector>
#include <stack>
#include <queue>
#include <math.h>
#include <set>
#include <map>
#include <string>
#include <tuple>
#include <numeric>
#include <climits>
#include <bitset>
#include <iomanip>
#include <random>
#include <ctime>
using namespace std;
typedef int ll;
ll max(ll a, ll b) {
if (a > b) {
return a;
} else {
return b;
}
}
ll min(ll a, ll b) {
if (a < b) {
return a;
} else {
return b;
}
}
const ll MAXN = 4001;
const ll MAXM = 2097153;
const ll MOD = 1e9 + 7;
const ll INF = 1e7;
ll h, w;
ll dr[4] = {1, 0, -1, 0};
ll dc[4] = {0, 1, 0, -1};
ll mark[MAXN][MAXN];
char grid[MAXN][MAXN];
ll cnt;
void dfs(ll row, ll col) {
for (ll k = 0; k < 4; k++) {
ll nr = row + dr[k];
ll nc = col + dc[k];
if (nr >= 0 && nr < h && nc >= 0 && nc < w && grid[nr][nc] == grid[row][col] && mark[nr][nc] == 0) {
mark[nr][nc] = cnt;
dfs(nr, nc);
}
}
}
void solve(ll ca) {
cin >> h >> w;
for (ll i = 0; i < h; i++) {
for (ll j = 0; j < w; j++) {
cin >> grid[i][j];
}
}
cnt = 1;
for (ll i = 0; i < h; i++) {
for (ll j = 0; j < w; j++) {
if (grid[i][j] != '.' && mark[i][j] == 0) {
//start a dfs
mark[i][j] = cnt;
dfs(i, j);
cnt++;
}
}
}
set<pair<ll, ll>> edges;
for (ll i = 0; i < h; i++) {
for (ll j = 0; j < w; j++) {
for (ll k = 0; k < 4; k++) {
ll nr = i + dr[k];
ll nc = j + dc[k];
if (nr >= 0 && nr < h && nc >= 0 && nc < w && mark[i][j] != mark[nr][nc]) {
edges.insert({mark[i][j], mark[nr][nc]});
}
}
}
}
vector<ll> adj[cnt];
for (auto el: edges) {
adj[el.first].push_back(el.second);
}
queue<pair<ll, ll>> q;
q.push({1, 0});
ll dist[cnt];
for (ll i = 0; i < cnt; i++) {
dist[i] = INF;
}
ll ans = 0;
while (!q.empty()) {
pair<ll, ll> cur = q.front();
q.pop();
if (dist[cur.first] != INF) {
continue;
}
ans = max(ans, cur.second);
dist[cur.first] = cur.second;
for (auto el: adj[cur.first]) {
if (dist[el] == INF) {
q.push({el, cur.second+1});
}
}
}
cout << ans+1 << endl;
}
int main() {
mt19937 rng(0);
// Fast IO
ios::sync_with_stdio(false);
cin.tie(nullptr);
/*
freopen("piggyback.in", "r", stdin);
freopen("piggyback.out", "w", stdout);
*/
ll t = 1;
//cin >> t;
ll co = 0;
while (t--) {
solve(co);
co++;
}
}
