#include <iostream>
#include <vector>
#include <deque>
using namespace std;
int main (void) {
iostream::sync_with_stdio(false);
cin.tie(0);
int dx[4] = {0, 0, 1, -1};
int dy[4] = {1, -1, 0, 0};
int N, M;
cin >> N >> M;
//vector<string> grid(N);
string grid[4000];
for (int i = 0; i < N; i++)
cin >> grid[i];
vector<vector<int>> dist(N, vector<int>(M, 0));
deque<vector<int>> bfs;
bfs.push_back({0, 0, 1});
int ans = 0;
while (!bfs.empty()) {
int x = bfs.front()[0], y = bfs.front()[1], d = bfs.front()[2];
bfs.pop_front();
dist[x][y] = d;
ans = max(ans, d);
for (int i = 0; i < 4; i++) {
int nx = x + dx[i], ny = y + dy[i];
if (nx < 0 || nx >= N || ny < 0 || ny >= M)
continue;
if (dist[nx][ny] != 0 || grid[nx][ny] == '.')
continue;
vector<int> next = {nx, ny, d};
if (grid[x][y] != grid[nx][ny]) {
next[2]++;
bfs.push_back(next);
} else
bfs.push_front(next);
}
}
/*for (auto x: dist) {
for (auto y: x) {
cout << y << " ";
}
cout << endl;
}*/
cout << ans << endl;
return 0;
}
