def solve():
	H,W = map(int,raw_input().split())
 	S = [raw_input() for i in xrange(H)]
	VD = [[H]*(W+2) for i in xrange(H+2)]
	HD = [[W]*(H+2) for j in xrange(W+2)]
	for i in xrange(H+2):
		for j in xrange(W+2):
			if not (0 < i <= H and 0 < j <= W) or S[i-1][j-1] == ".":
				VD[i][j] = HD[j][i] = 0

	for i in xrange(1,H+1):
		for j in xrange(1,W+1):
			VD[i][j] = min(VD[i][j],min(VD[i-1][j-1:j+2])+1)
			VD[H+1-i][j] = min(VD[H+1-i][j],min(VD[H+2-i][j-1:j+2])+1)
	for j in xrange(1,W+1):
		for i in xrange(1,H+1):
			HD[j][i] = min(HD[j][i],min(HD[j-1][i-1:i+2])+1)
			HD[W+1-j][i] = min(HD[W+1-j][i],min(HD[W+2-j][i-1:i+2])+1)
	ans = 0
	for i in xrange(1,H+1):
		for j in xrange(1,W+1):
			ans = max(ans,min(VD[i][j],HD[j][i]))
	print ans
solve()