#include <bits/stdc++.h>
using namespace std;
int main() {
iostream::sync_with_stdio(false);
cin.tie(0);
int h, w;
cin >> h >> w;
vector<vector<char> > graph(h, vector<char>(w, 0));
for (int i = 0; i < h; i++) {
for (int j = 0; j < w; j++) {
cin >> graph[i][j];
}
}
deque<vector<int> > bfs;
bfs.push_back({0, 0});
vector<vector<int> > dist(h, vector<int>(w, -1));
dist[0][0] = 1;
int ans = 0;
vector<pair<int, int> > vec = {{0, 1}, {1, 0}, {0, -1}, {-1, 0}};
while (!bfs.empty()) {
auto current = bfs.front();
bfs.pop_front();
ans = max(ans, dist[current[0]][current[1]]);
// cout << current[0] << current[1] << dist[current[0]][current[1]] << endl;
for (pair<int, int> val: vec) {
int newx = current[0] + val.first;
int newy = current[1] + val.second;
if (newx >= 0 &&
newx < h &&
newy < w &&
newy >= 0) {
if (graph[newx][newy] == '.' || dist[newx][newy] != -1) continue;
if (graph[newx][newy] ==
graph[current[0]][current[1]]) {
dist[newx][newy] = dist[current[0]][current[1]];
bfs.push_front({newx, newy});
} else {
bfs.push_back({newx, newy});
dist[newx][newy] = dist[current[0]][current[1]] + 1;
}
}
}
}
cout << ans << endl;
}
