h,w=map(int,input().split())
s=[input()for _ in[0]*h]
a=1e5
for i in s:
	c=0
	for j in i:
		if j=='.'and c:a=min(a,c);c=0
		if'#'==j:c+=1
	if c:a=min(a,c)
for i in range(w):
	c=0
	for j in range(h):
		if'.'==s[j][i]and c:a=min(a,c);c=0
		if'#'==s[j][i]:c+=1
	if c:a=min(a,c)
print(a)