You are given two matrices A and B. Each matrix contains exactly n rows and m columns. Each element of A is either 0 or 1; each element of B is initially 0.

You may perform some operations with matrix B. During each operation, you choose any submatrix of B having size 2 × 2, and replace every element in the chosen submatrix with 1. In other words, you choose two integers x and y such that 1 ≤ x < n and 1 ≤ y < m, and then set B_{x, y}, B_{x, y + 1}, B_{x + 1, y} and B_{x + 1, y + 1} to 1.

Your goal is to make matrix B equal to matrix A. Two matrices A and B are equal if and only if every element of matrix A is equal to the corresponding element of matrix B.

Is it possible to make these matrices equal? If it is, you have to come up with a sequence of operations that makes B equal to A. Note that you don't have to minimize the number of operations.

Input

The first line contains two integers n and m (2 ≤ n, m ≤ 50).

Then n lines follow, each containing m integers. The j-th integer in the i-th line is A_{i, j}. Each integer is either 0 or 1.

Output

If it is impossible to make B equal to A, print one integer -1.

Otherwise, print any sequence of operations that transforms B into A in the following format: the first line should contain one integer k — the number of operations, and then k lines should follow, each line containing two integers x and y for the corresponding operation (set B_{x, y}, B_{x, y + 1}, B_{x + 1, y} and B_{x + 1, y + 1} to 1). The condition 0 ≤ k ≤ 2500 should hold.

Examples

Input


3 3
1 1 1
1 1 1
0 1 1


Output


3
1 1
1 2
2 2


Input


3 3
1 0 1
1 0 1
0 0 0


Output


-1


Input


3 2
0 0
0 0
0 0


Output


0

Note

The sequence of operations in the first example:

\begin{matrix} 0 & 0 & 0 & & 1 & 1 & 0 & & 1 & 1 & 1 & & 1 & 1 & 1 \\\ 0 & 0 & 0 & → & 1 & 1 & 0 & → & 1 & 1 & 1 & → & 1 & 1 & 1 \\\ 0 & 0 & 0 & & 0 & 0 & 0 & & 0 & 0 & 0 & & 0 & 1 & 1 \end{matrix} 
n, m = [int(x) for x in str(input('')).split(' ')]

A = [ [ 0 for i in range(m) ] for j in range(n) ]
B = [ [ 0 for i in range(m) ] for j in range(n) ]
D = [ [ 0 for i in range(m) ] for j in range(n) ]

for i in range (0, n):
    A[i] = [int(x) for x in str(input('')).split(' ')]
    
C = [row[:] for row in A]

possible = True
for i in range (0, n-1):
    for j in range (0, m-1):
        
        quater_sum = A[i][j] + A[i][j+1] + A[i+1][j] + A[i+1][j+1]
        if quater_sum > 0:
            if quater_sum != 4:
                pass
            else:
                C[i][j], C[i][j+1], C[i+1][j], C[i+1][j+1] = 0, 0, 0, 0
                D[i][j] = 1
            if C[i][j]:
                possible = False
                break

    if not possible:
        break
        
if sum(sum(C,[])):
    possible = False
    
if not possible:
    print("-1")
else:
    ans = sum(sum(D,[]))
    try:
        print(ans)
        for i in range (0, n):
            for j in range (0, m):
                if D[i][j]:
                    print(i+1, j+1)
    except:
        pass