/**
* In the name of GOD
* author : Behradm
**/
#include "bits/stdc++.h"
using namespace std;
#define sz(x) (int) ((x).size())
short dx[4] = {0, 0, 1, -1};
short dy[4] = {1, -1, 0, 0};
const int N = 4e3 + 3;
char s[N][N];
int tag[N][N];
vector<vector<pair<int, int>>> pep;
vector<int> h;
queue<int> q;
int n, m;
bool Good(int x, int y) {
return (0 <= x && x < n && 0 <= y && y < m && s[x][y] != '.');
}
void dfs1(int i, int j, int c) {
tag[i][j] = c;
for (int k = 0; k < 4; k++) {
int x = i + dx[k], y = j + dy[k];
if (Good(x, y) && s[x][y] == s[i][j] && tag[x][y] == -1) {
dfs1(x, y, c);
}
}
}
void dfs2(int i, int j, int c) {
bool ok = 1;
for (int k = 0; k < 4; k++) {
int x = i + dx[k], y = j + dy[k];
if (Good(x, y) && s[x][y] != s[i][j])
ok = 0;
}
if (!ok)
pep[c].push_back({i, j});
tag[i][j] = c;
for (int k = 0; k < 4; k++) {
int x = i + dx[k], y = j + dy[k];
if (Good(x, y) && s[x][y] == s[i][j] && tag[x][y] == -1) {
dfs2(x, y, c);
}
}
}
signed main() {
ios::sync_with_stdio(false);
cin.tie(0);
cin >> n >> m;
if (n == 1 && m == 1)
return cout << 1 << '\n', 0;
memset(tag, -1, sizeof tag);
for (int i = 0; i < n; i++) {
for (int j = 0; j < m; j++) {
cin >> s[i][j];
}
}
int c = 0;
for (int i = 0; i < n; i++) {
for (int j = 0; j < m; j++) {
if (tag[i][j] == -1 && s[i][j] != '.')
dfs1(i, j, c++);
}
}
pep.resize(c);
h.resize(c);
memset(tag, -1, sizeof tag);
c = 0;
for (int i = 0; i < n; i++) {
for (int j = 0; j < m; j++) {
if (tag[i][j] == -1 && s[i][j] != '.')
dfs2(i, j, c++);
}
}
q.push(0), h[0] = 1;
int ans = 1;
while (!q.empty()) {
int u = q.front();
q.pop();
for (auto [i, j] : pep[u]) {
for (int k = 0; k < 4; k++) {
int x = i + dx[k], y = j + dy[k];
if (Good(x, y) && s[x][y] != s[i][j]) {
int v = tag[x][y];
if (h[v] == 0) {
q.push(v);
h[v] = h[u] + 1;
ans = max(ans, h[v]);
}
}
}
}
}
cout << ans << '\n';
return 0;
}
