#include <stdio.h>

int h, w;
int f[3002][3002];

int queue[9000000], get, set;

int main() {
	scanf("%d%d", &h, &w);
	for(int i = 1; i <= h; i++) {
		char s[3002];
		scanf("%s", s + 1);
		for(int j = 1; j <= w; j++) {
			f[i][j] = (s[j] == '.' ? 0 : -1);
		}
	}
	
	for(int i = 0; i <= h + 1; i++) {
	for(int j = 0; j <= w + 1; j++) {
		if(f[i][j] == 0) {
			for(int k = -1; k <= 1; k++) {
			for(int l = -1; l <= 1; l++) {
				if(k == 0 && l == 0) { continue; }
				if( ! (1 <= i + k && i + k <= h && 1 <= j + l && j + l <= w) ) { continue; }
				
				if(f[i + k][j + l] == -1) {
					f[i + k][j + l] = 1;
					queue[set++] = (i + k) * 4000 + (j + l);
				}
			}
			}
		}
	}
	}
	
	int max = 1;
	while(get != set) {
		int q = queue[get++];
		int i = q / 4000;
		int j = q % 4000;
		for(int k = -1; k <= 1; k++) {
		for(int l = -1; l <= 1; l++) {
			if(k == 0 && l == 0) { continue; }
			
			if(f[i + k][j + l] == -1) {
				f[i + k][j + l] = f[i][j] + 1;
				if(max < f[i][j] + 1) { max = f[i][j] + 1; }
				queue[set++] = (i + k) * 4000 + (j + l);
			}
		}
		}
	}
	
	printf("%d\n", max);
	
	return 0;
}