#include <iostream>
#include <vector>
using namespace std;
const int INF = 10000;
int main(){
	int H, W;
	cin >> H >> W;
	vector<vector<char>> S(H + 2, vector<char>(W + 2, '.'));
	for (int i = 1; i <= H; i++){
		for (int j = 1; j <= W; j++){
			cin >> S[i][j];
		}
	}
	vector<vector<int>> U(H + 2, vector<int>(W + 2, 0));
	for (int i = 1; i <= H; i++){
		for (int j = 1; j <= W; j++){
			if (S[i][j] == '#'){
				U[i][j] = U[i - 1][j] + 1;
			}
		}
	}
	vector<vector<int>> D(H + 2, vector<int>(W + 2, 0));
	for (int i = H; i >= 1; i--){
		for (int j = 1; j <= W; j++){
			if (S[i][j] == '#'){
				D[i][j] = D[i + 1][j] + 1;
			}
		}
	}
	vector<vector<int>> L(H + 2, vector<int>(W + 2, 0));
	for (int j = 1; j <= W; j++){
		for (int i = 1; i <= H; i++){
			if (S[i][j] == '#'){
				L[i][j] = L[i][j - 1] + 1;
			}
		}
	}
	vector<vector<int>> R(H + 2, vector<int>(W + 2, 0));
	for (int j = W; j >= 1; j--){
		for (int i = 1; i <= H; i++){
			if (S[i][j] == '#'){
				R[i][j] = R[i][j + 1] + 1;
			}
		}
	}
	int ans = 0;
	for (int i = 1; i <= H; i++){
		for (int j = 1; j <= W; j++){
			int mn = INF;
			mn = min(mn, U[i][j]);
			mn = min(mn, D[i][j]);
			mn = min(mn, L[i][j]);
			mn = min(mn, R[i][j]);
			ans = max(ans, mn);
		}
	}
	cout << ans << endl;
}