#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]; } memset(d, 0x3f, sizeof d); deque<tuple<int, int, int>> dq; int ans = 1; d[1][1] = 1; dq.push_back({1, 1, d[1][1]}); while (dq.size()) { auto [x, y, dist] = dq.front(); dq.pop_front(); ans = max(ans, d[x][y]); // cout << x << ' ' << y << '\n'; if (dist > d[x][y]) { continue; } for (int i = 0; i < 4; i += 1) { int newx = x + dx[i], newy = y + dy[i]; if (inside(newx, newy)) { if (a[x][y] == a[newx][newy]) { if (d[newx][newy] > dist) { d[newx][newy] = dist; dq.push_front({newx, newy, d[newx][newy]}); } } else { if (d[newx][newy] > dist + 1) { d[newx][newy] = dist + 1; dq.push_back({newx, newy, d[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; }