Golu is given a task of clearing coins fallen down  on floor. Naughty being his modus operandi, he thought of playing a game while clearing coins. He arranges the coins like an M X N matrix with random heads (1) and tails (0).

In every move, he chooses a sub-matrix of size L X B [such that max(L,B) >1] and interchanges all heads to tails and vice-versa present in the chosen sub-matrix. Then if he finds a 2X2 sub-matrix exclusively of heads anywhere in the M X N matrix, he removes those coins.

Your task is simple. You have to report the minimum no. of moves taken by him before he clears his first 2X2 sub-matrix.

Input:

Your first line of input consists of two numbers M, N. Each of the next M lines consists of N space-separated integers which are either 0 or 1.

Output:

Output a single line answer giving the minimum no. of steps taken before his first clearance. If it is impossible for him to do so, print "-1" (quotes for clarity).

Constraints :

2 ≤ M,N ≤ 10

Author : Srinivas

Testers : Shubham Parekh , Shreyans

(By IIT Kgp HackerEarth Programming Club)

SAMPLE INPUT
2 4
0 0 1 1
0 0 1 1

SAMPLE OUTPUT
0
M,N=map(int,raw_input().split())
L=[]
for i in range(M):
    L.append(map(int,raw_input().split()))

if M+N==4 and (L==[[0,1],[1,1]] or L==[[1,0],[1,1]] or L==[[1,1],[1,0]] or L==[[1,1],[0,1]]) or L==[[1,0],[0,0]] or L==[[0,1],[0,0]] or L==[[0,0],[1,0]] or L==[[0,0],[0,1]]:
        print "-1"
else:
    List=[]
    for i in range(M-1):
        for j in range(N-1):
            List.append(([L[i][j],L[i][j+1],L[i+1][j],L[i+1][j+1]],[j!=0,j+2!=N,i!=0,i+2!=M]))   #L,R,T,B
    zero=False
    one=False
    for i in List:
        if i[0]==[1,1,1,1]:
            zero=True
            print "0"
            break
        elif i[0]==[0,0,0,0] or i[0]==[1,0,1,0] or i[0]==[1,1,0,0] or i[0]==[0,1,0,1] or i[0]==[0,0,1,1] or (i[0]==[0,1,1,1] and (i[1][0] or i[1][2])) or (i[0]==[1,0,1,1] and (i[1][1] or i[1][2])) or (i[0]==[1,1,0,1] and (i[1][0] or i[1][3])) or (i[0]==[1,1,1,0] and (i[1][1] or i[1][3])):
            one=True
    if (not zero):
        if (one):
            print "1"
        else:
            print "2"