#include <bits/stdc++.h>
using namespace std;
int h, w, curr = 1, max_depth = 1;
int a[4002][4002];
bool b[4002][4002];
char ss;
vector<pair<int, int>> dif;
int label[4002][4002];
vector<set<int>> adj;
void fill(int start_i, int start_j) {
queue<pair<int, int>> q;
q.push({start_i, start_j});
b[start_i][start_j] = 1;
label[start_i][start_j] = curr;
while (!q.empty()) {
auto [i, j] = q.front();
q.pop();
for (auto x : dif) {
int i_next = i + x.first, j_next = j + x.second;
if (i_next <= h && i_next >= 1 && j_next <= w && j_next >= 1) {
if (a[i][j] == a[i_next][j_next] && !b[i_next][j_next]) {
b[i_next][j_next] = 1;
label[i_next][j_next] = curr;
q.push({i_next, j_next});
} else if (b[i_next][j_next] && a[i][j] != a[i_next][j_next] &&
a[i_next][j_next] != '.') {
adj[label[i][j]].insert(label[i_next][j_next]);
adj[label[i_next][j_next]].insert(label[i][j]);
}
}
}
}
}
void find_max_shortest_path(int startNode) {
vector<int> dist(curr + 1, -1);
queue<int> q;
q.push(startNode);
dist[startNode] = 1;
while (!q.empty()) {
int u = q.front();
q.pop();
max_depth = max(max_depth, dist[u]);
for (int neighbor : adj[u]) {
if (dist[neighbor] == -1) {
dist[neighbor] = dist[u] + 1;
q.push(neighbor);
}
}
}
}
int main() {
adj.emplace_back(set<int>{0});
dif.emplace_back(1, 0);
dif.emplace_back(-1, 0);
dif.emplace_back(0, 1);
dif.emplace_back(0, -1);
cin >> h >> w;
for (int i = 1; i <= h; i++) {
for (int j = 1; j <= w; j++) {
cin >> ss;
a[i][j] = ss;
}
}
for (int i = 1; i <= h; i++) {
for (int j = 1; j <= w; j++) {
if (a[i][j] == '.') {
b[i][j] = 1;
} else {
if (!b[i][j]) {
adj.emplace_back(set<int>{});
fill(i, j);
curr++;
}
}
}
}
if (a[1][1] == '.') {
cout << 0 << "\n";
return 0;
} else {
find_max_shortest_path(1);
cout << max_depth << "\n";
}
return 0;
}
