m,n=map(int,input().split())
A=[]
for i in range(0,m):
	B=list(map(int,input().split()))
	A.append(B)
 
dodai = 0
 
for i in range(0,m):
	for j in range(0,n):
		for k in range(1, n): #độ dài cạnh
			if i + k - 1 < m and j + k - 1 < n:
				x = i
				y = j #tọa độ góc trên (x, y)
				u = i + k - 1
				v = j + k - 1 # tọa độ góc dưới (u, v)
 
				bangNhau = True
				for a in range(x, u + 1):
					for b in range(y, v + 1):
						if A[a][b] != A[x][y]:
							bangNhau = False
 
				if bangNhau == True:
					#thỏa mãn
					dodai = max(dodai, k)
print(dodai)

bSxuPW1hcChpbnQsaW5wdXQoKS5zcGxpdCgpKQpBPVtdCmZvciBpIGluIHJhbmdlKDAsbSk6CglCPWxpc3QobWFwKGludCxpbnB1dCgpLnNwbGl0KCkpKQoJQS5hcHBlbmQoQikKCmRvZGFpID0gMAoKZm9yIGkgaW4gcmFuZ2UoMCxtKToKCWZvciBqIGluIHJhbmdlKDAsbik6CgkJZm9yIGsgaW4gcmFuZ2UoMSwgbik6ICPEkeG7mSBkw6BpIGPhuqFuaAoJCQlpZiBpICsgayAtIDEgPCBtIGFuZCBqICsgayAtIDEgPCBuOgoJCQkJeCA9IGkKCQkJCXkgPSBqICN04buNYSDEkeG7mSBnw7NjIHRyw6puICh4LCB5KQoJCQkJdSA9IGkgKyBrIC0gMQoJCQkJdiA9IGogKyBrIC0gMSAjIHThu41hIMSR4buZIGfDs2MgZMaw4bubaSAodSwgdikKCQoJCQkJYmFuZ05oYXUgPSBUcnVlCgkJCQlmb3IgYSBpbiByYW5nZSh4LCB1ICsgMSk6CgkJCQkJZm9yIGIgaW4gcmFuZ2UoeSwgdiArIDEpOgoJCQkJCQlpZiBBW2FdW2JdICE9IEFbeF1beV06CgkJCQkJCQliYW5nTmhhdSA9IEZhbHNlCgkKCQkJCWlmIGJhbmdOaGF1ID09IFRydWU6CgkJCQkJI3Ro4buPYSBtw6NuCgkJCQkJZG9kYWkgPSBtYXgoZG9kYWksIGspCnByaW50KGRvZGFpKQ==

MTEgMTMKMCAwIDAgMCAwIDEgMCAwIDAgMCAwIDAgMAowIDAgMCAwIDEgMSAxIDAgMCAwIDAgMCAwCjAgMCAxIDEgMSAxIDEgMSAxIDAgMCAwIDAKMCAwIDEgMSAxIDEgMSAxIDEgMCAwIDAgMAowIDEgMSAxIDEgMSAxIDEgMSAxIDAgMCAwCjEgMSAxIDEgMSAxIDEgMSAxIDEgMSAwIDAKMCAxIDEgMSAxIDEgMSAxIDEgMSAwIDAgMAowIDAgMSAxIDEgMSAxIDEgMSAwIDAgMCAwCjAgMCAxIDEgMSAxIDEgMSAxIDAgMCAwIDAKMCAwIDAgMCAxIDEgMSAwIDAgMCAwIDEgMQowIDAgMCAwIDAgMSAwIDAgMCAwIDAgMSAxCg==

11 13
0 0 0 0 0 1 0 0 0 0 0 0 0
0 0 0 0 1 1 1 0 0 0 0 0 0
0 0 1 1 1 1 1 1 1 0 0 0 0
0 0 1 1 1 1 1 1 1 0 0 0 0
0 1 1 1 1 1 1 1 1 1 0 0 0
1 1 1 1 1 1 1 1 1 1 1 0 0
0 1 1 1 1 1 1 1 1 1 0 0 0
0 0 1 1 1 1 1 1 1 0 0 0 0
0 0 1 1 1 1 1 1 1 0 0 0 0
0 0 0 0 1 1 1 0 0 0 0 1 1
0 0 0 0 0 1 0 0 0 0 0 1 1