import sys
h,w=map(int,raw_input().split());r=1
S=[[1-ord(c)/46 for c in e.strip()] for e in sys.stdin]
for y in range(1,h):
 for x in range(1,w):
  q=-~min(S[y-1][x-1],S[y][x-1],S[y-1][x])*S[y][x];S[y][x]=q;r=max(r,q)
print -~r/2