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

using namespace std;

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

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

int main(){
	int H,W,MAX,ans = 0;
	scanf("%d %d",&H,&W);
	rep(i,H) scanf("%s",S[i]);
	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;
}