#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));
for (int i = 0; i < h; ++i) {
for (int j = 0; j < w; ++j) cin >> grid[i][j];
}
vector<pair<int, int>> directions = {{-1, 0}, {1, 0}, {0, -1}, {0, 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 : directions) {
int newX = (cur / w) + i.first, newY = (cur % w) + i.second,
newVal = newX * w + newY;
if (newX < 0 || newX >= h || newY < 0 || newY >= w) continue;
if (distances[newVal] != -1) continue;
if (grid[newX][newY] == '.') continue;
distances[newVal] =
distances[cur] + (grid[newX][newY] != grid[cur / w][cur % w]);
if ((grid[newX][newY] != grid[cur / w][cur % w]))
q.push_back(newVal);
else
q.push_front(newVal);
}
}
int res = 0;
for (auto &i : distances) res = max(res, (int)i);
cout << res << '\n';
return 0;
}
