import sys
h,w=map(int,raw_input().split());r=0
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):
  S[y][x]+=min(S[y-1][x-1],S[y][x-1],S[y-1][x])*S[y][x];r=max(r,S[y][x])
print -~r/2