#include <bits/stdc++.h> using namespace std; #define ll long long #define maxn 4005 #define mod 1000000007 int h, w, d[maxn][maxn], dx[] = {-1, 1, 0, 0}, dy[] = {0, 0, -1, 1}; char a[maxn][maxn]; bool inside(int x, int y) { return (x >= 1 && x <= h && y >= 1 && y <= w && a[x][y] != '.'); } void solve() { cin >> h >> w; for (int i = 1; i <= h; i += 1) for (int j = 1; j <= w; j += 1) { cin >> a[i][j]; } deque<pair<int, int>> dq; int ans = 1; d[1][1] = 1; dq.push_back({1, 1}); while (dq.size()) { auto [x, y] = dq.front(); dq.pop_front(); // cout << x << ' ' << y << ' ' << d[x][y] << '\n'; ans = max(ans, d[x][y]); for (int i = 0; i < 4; i += 1) { int newx = x + dx[i], newy = y + dy[i]; if (inside(newx, newy) && d[newx][newy] == 0) { if (a[x][y] == a[newx][newy]) { d[newx][newy] = d[x][y]; dq.push_front({newx, newy}); } else { d[newx][newy] = d[x][y] + 1; dq.push_back({newx, newy}); } } } } cout << ans; return; } int main() { ios_base::sync_with_stdio(0); cin.tie(0); cout.tie(0); int test_case = 1; // cin >> test_case; for (int i = 1; i <= test_case; i += 1) { solve(); } return 0; }