def solve():
	H,W = map(int,raw_input().split())
	S = []
	elem = {".","#"}
	for i in xrange(H):
		s = raw_input()
		assert len(s) == W
		assert len(elem | set(s)) == 2
 		S.append(s)
	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] = 1 + min(VD[i][j]-1,VD[i-1][j-1],VD[i-1][j],VD[i-1][j+1])
			VD[H+1-i][j] = 1 + min(VD[H+1-i][j]-1,VD[H+2-i][j-1],VD[H+2-i][j],VD[H+2-i][j+1])
	for j in xrange(1,W+1):
		for i in xrange(1,H+1):
			HD[j][i] = 1 + min(HD[j][i]-1,HD[j-1][i-1],HD[j-1][i],HD[j-1][i+1])
			HD[W+1-j][i] = 1 + min(HD[W+1-j][i]-1,HD[W+2-j][i-1],HD[W+2-j][i],HD[W+2-j][i+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()