#include <bits/stdc++.h> #pragma GCC Optimize("Ofast") using namespace std; #define fast_cin() ios_base::sync_with_stdio(false); cin.tie(NULL); cout.tie(NULL) int depth[4005][4005]; string s[4000]; int main() { fast_cin(); int h, w; cin >> h >> w; for (int i = 0; i < h; i++) cin >> s[i]; deque<pair<int, int>> q; depth[0][0] = 1; q.push_back({0, 0}); vector<pair<int, int>> dir = {{-1, 0}, {1, 0}, {0, -1}, {0, 1}}; auto inside = [&](int x, int y) { return x >= 0 && x < h && y >= 0 && y < w && s[x][y] != '.'; }; int ans = 1; while (!q.empty()) { auto [x, y] = q.front(); q.pop_front(); ans = max(ans, depth[x][y]); for (auto [dx, dy] : dir) { int nx = x + dx, ny = y + dy; if (inside(nx, ny) && depth[nx][ny] == 0) { if (s[x][y] == s[nx][ny]) { depth[nx][ny] = depth[x][y]; q.push_front({nx, ny}); } else { depth[nx][ny] = depth[x][y] + 1; q.push_back({nx, ny}); } } } } cout << ans << endl; }