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 = map(int, input().split())
matra = []
for i in range(n):
    matra.append(list(map(int, input().split())))
matrb = [[0]*m for i in range(n)]

res = []
t = True
anumbs = ((-1, -1), (0, -1), (-1, 0), (0, 0))
for i in range(n):
    for j in range(m):
        if matra[i][j] != matrb[i][j]:
            matrb[i][j] = matra[i][j]
            a = [[], [], [], []]
            if i-1 >= 0 and j-1 >= 0:
                a[0] = [matra[i-1][j], matra[i][j-1], matra[i-1][j-1]]
            if i+1 < n and j-1 >= 0:
                a[1] = [matra[i+1][j], matra[i][j-1], matra[i+1][j-1]]
            if i-1 >= 0 and j+1 < m:
                a[2] = [matra[i-1][j], matra[i][j+1], matra[i-1][j+1]]
            if i + 1 < n and j + 1 < m:
                a[3] = [matra[i + 1][j], matra[i][j + 1], matra[i + 1][j + 1]]
            for k in range(len(a)):
                if a[k] == [1, 1, 1]:
                    res.append([i + anumbs[k][0] + 1, j + anumbs[k][1] + 1])
                    if k == 0:
                        matrb[i - 1][j], matrb[i][j - 1], matrb[i - 1][j - 1] = 1, 1, 1
                    elif k == 1:
                        matrb[i + 1][j], matrb[i][j - 1], matrb[i + 1][j - 1] = 1, 1, 1
                    elif k == 2:
                        matrb[i - 1][j], matrb[i][j + 1], matrb[i - 1][j + 1] = 1, 1, 1
                    else:
                        matrb[i + 1][j], matrb[i][j + 1], matrb[i + 1][j + 1] = 1, 1, 1
                    break
            else:
                t = False
                break
    else:
        continue
    break

if t:
    print(len(res))
    for i in range(len(res)):
        print(*res[i])
else:
    print(-1)