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