#include <bits/stdc++.h>
using namespace std;
int dx[4] = {0, 0, -1, 1};
int dy[4] = {-1, 1, 0, 0};
int main() {
int h, w;
cin >> h >> w;
vector<vector<char>> grid(h, vector<char>(w));
int cnt = 0;
for (int i = 0; i < h; i++) {
for (int j = 0; j < w; j++) {
cin >> grid[i][j];
if (grid[i][j] != '.') cnt++;
}
}
deque<pair<int, int>> dq;
vector<vector<int>> dist(h, vector<int>(w, 0x3f3f3f3f));
// vector<vector<int>> vis(h, vector<int>(w));
dist[0][0] = 0;
dq.push_front({0, 0});
while (!dq.empty()) {
auto tp = dq.front();
dq.pop_front();
// cout << 61 - cnt << "\t" << tp.first << " " << tp.second << endl;
cnt--;
if (cnt == 0) {
break;
}
for (int i = 0; i < 4; i++) {
int nx = tp.first + dx[i];
int ny = tp.second + dy[i];
if (nx < 0 || nx >= h || ny < 0 || ny >= w) continue;
if (grid[nx][ny] == '.') continue;
int cost = 1;
if (grid[nx][ny] == grid[tp.first][tp.second]) cost = 0;
// cout << vis[nx][ny] << " " << nx << " " << ny << endl;
if (dist[tp.first][tp.second] + cost < dist[nx][ny]) {
// vis[nx][ny] = true;
dist[nx][ny] = dist[tp.first][tp.second] + cost;
if (cost == 1) {
dq.push_back({nx, ny});
} else {
dq.push_front({nx, ny});
}
}
}
}
int ans = 0;
for (int i = 0; i < h; i++) {
for (int j = 0; j < w; j++) {
if (grid[i][j] != '.') ans = max(ans, dist[i][j]);
}
cout << endl;
}
cout << ans + 1 << endl;
}
