#include <stdio.h>
#include <iostream>
#include <string>
#include <vector>

using namespace std;

#define range(i,a,b) for(int i=(a); i < (b); i++)
#define rep(i,n) range(i,0,n)

int VD[3002][3002],HD[3002][3002];

int main(){
	int H,W,MAX,ans = 0;
	vector <string> S;
	scanf("%d %d",&H,&W);
	S = vector <string> (H);
	if ((H < 1)||(H > 3000)){throw "H is bad!";}
	if ((W < 1)||(W > 3000)){throw "W is bad!";}
	rep(i,H){
		cin >> S[i];
		if(S[i].size() != W){throw "row size";}
		rep(j,W){
			if((S[i][j] != '#') && (S[i][j] != '.')){throw "row element";}
		}
	}
	MAX = max(H,W);
	rep(i,H+2) rep(j,W+2){
			if (i < 1 || i > H || j < 1 || j > W)
				VD[i][j] = HD[j][i] = 0;
			else
				VD[i][j] = HD[j][i] = (S[i-1][j-1] == '.' ? 0 : MAX);
	}
	range(i,1,H+1) range(j,1,W+1) rep(k,3){
		VD[i][j] = min(VD[i][j],VD[i-1][j-1+k]+1);
		VD[H+1-i][j] = min(VD[H+1-i][j],VD[H+2-i][j-1+k]+1);
	}
	range(j,1,W+1) range(i,1,H+1) rep(k,3){
		HD[j][i] = min(HD[j][i],HD[j-1][i-1+k]+1);
		HD[W+1-j][i] = min(HD[W+1-j][i],HD[W+2-j][i-1+k]+1);
	}
	range(i,1,H+1) range(j,1,W+1){
		ans = max(ans,min(VD[i][j],HD[j][i]));
	}
	printf("%d\n",ans);
	return 0;
}