//サンプルがやさしい(な阪関) #include <iostream> #include <algorithm> #include <tuple> #include <queue> #include <cstdio> using namespace std; int h, w; char s[3002][3002]; int dy[8] = {-1, -1, -1, 0, 0, 1, 1, 1}; int dx[8] = {-1, 0, 1, -1, 1, -1, 0, 1}; int cost[3002][3002]; void input() { //番兵する cin >> h >> w; h += 2; w += 2; for (int i = 0; i < h; i++) { for (int j = 0; j < w; j++) { s[i][j] = '.'; } } for (int i = 1; i < h - 1; i++) { scanf("%s", s[i] + 1); s[i][w-1] = '.'; } for (int i = 0; i < h; i++) { for (int j = 0; j < w; j++) { cost[i][j] = 1145141919; } } } bool is_range(int y, int x) { return (0 <= y && y < h && 0 <= x && x < w); } void bfs() { typedef tuple<int, int, int> T; //cost, y, x static queue<T> que; //全ての海を始点にする for (int i = 0; i < h; i++) { for (int j = 0; j < w; j++) { if (s[i][j] == '.') { que.push(T(0, i, j)); cost[i][j] = 0; } } } while (!que.empty()) { T now = que.front(); que.pop(); int cst = get<0>(now); int y = get<1>(now); int x = get<2>(now); for (int dir = 0; dir < 8; dir++) { int ny = y + dy[dir]; int nx = x + dx[dir]; if (is_range(ny, nx) && cost[ny][nx] > cst + 1) { que.push(T(cst + 1, ny, nx)); cost[ny][nx] = cst + 1; } } } } int answer() { int ans = -1; for (int i = 0; i < h; i++) { for (int j = 0; j < w; j++) { ans = max(ans, cost[i][j]); } } return ans; } int main() { input(); bfs(); cout << answer() << endl; return 0; }