#include <bits/stdc++.h>
using namespace std;
int main() {
ios_base::sync_with_stdio(0);
cin.tie(0);
int h, w;
cin >> h >> w;
vector<vector<char>> grid(h, vector<char>(w, 0));
vector<vector<pair<int, bool>>> adjacency(h * w);
for (int i = 0; i < h; ++i) {
for (int j = 0; j < w; ++j) {
cin >> grid[i][j];
if (grid[i][j] == '.') continue;
if (i && grid[i - 1][j] != '.') {
if (grid[i - 1][j] == grid[i][j]) {
adjacency[i * w - w + j].emplace_back(i * w + j, 0);
adjacency[i * w + j].emplace_back(i * w - w + j, 0);
} else {
adjacency[i * w - w + j].emplace_back(i * w + j, 1);
adjacency[i * w + j].emplace_back(i * w - w + j, 1);
}
}
if (j && grid[i][j - 1] != '.') {
if (grid[i][j - 1] == grid[i][j]) {
adjacency[i * w - 1 + j].emplace_back(i * w + j, 0);
adjacency[i * w + j].emplace_back(i * w - 1 + j, 0);
} else {
adjacency[i * w - 1 + j].emplace_back(i * w + j, 1);
adjacency[i * w + j].emplace_back(i * w - 1 + j, 1);
}
}
}
}
vector<int> distances(h * w, -1);
distances[0] = 1;
deque<int> q;
q.push_front(0);
while (!q.empty()) {
int cur = q.front();
q.pop_front();
for (auto &i : adjacency[cur]) {
if (distances[i.first] != -1) continue;
distances[i.first] = distances[cur] + i.second;
if (i.second)
q.push_back(i.first);
else
q.push_front(i.first);
}
}
int res = 0;
for (auto &i : distances) res = max(res, i);
cout << res << '\n';
return 0;
}
