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