#include <bits/stdc++.h>
using namespace std;
int main(){
ios::sync_with_stdio(false);
cin.tie(nullptr);
cout.tie(nullptr);
int H, W;
cin >> H >> W;
vector<string> grid(H);
for (int i = 0; i < H; ++i) cin >> grid[i];
deque<pair<int, int>> frontier;
vector<vector<int>> dist(H, vector<int>(W, INT_MAX));
auto next_node = [&](const pair<int, int> &node) -> vector<pair<int, int>>{
vector<pair<int, int>> nxt;
if (node.first > 0) nxt.push_back({node.first - 1, node.second});
if (node.first < H - 1) nxt.push_back({node.first + 1, node.second});
if (node.second > 0) nxt.push_back({node.first, node.second - 1});
if (node.second < W - 1) nxt.push_back({node.first, node.second + 1});
return nxt;
};
frontier.push_back({0, 0});
dist[0][0] = 0;
while (!frontier.empty()){
pair<int, int> u = frontier.front();
frontier.pop_front();
for (pair<int, int> v : next_node(u)){
if (grid[v.first][v.second] == '.') continue;
if (grid[v.first][v.second] == grid[u.first][u.second]){
if (dist[u.first][u.second] < dist[v.first][v.second]){
dist[v.first][v.second] = dist[u.first][u.second];
frontier.push_front(v);
}
}
else {
if (dist[u.first][u.second] + 1 < dist[v.first][v.second]){
dist[v.first][v.second] = dist[u.first][u.second] + 1;
frontier.push_back(v);
}
}
}
}
int ans = 0;
for (int r = 0; r < H; ++r){
for (int c = 0; c < W; ++c){
if (dist[r][c] != INT_MAX){
ans = max(ans, dist[r][c]);
}
}
}
cout << ans + 1;
return 0;
}
