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, raw_input().split())
a = [[0] * m for i in range(n)]
ans = []


def check(inx):
    # print "Check for %s" % (inx,)
    coords = [(0, 0,), (1, 1,), (0, 1,), (1, 0,)]
    can = True
    for coord in coords:
        x, y = inx[0] + coord[0], inx[1] + coord[1]
        if (x >= n or y >= m) or not a[x][y]:
            can = False
            # print "It can't for {0}".format(inx)
            break
    if can:
        # print "It can for {0}".format(inx)
        return True
    return False


def do(inx):
    coords = [(0, 0,), (1, 1,), (0, 1,), (1, 0,)]
    for coord in coords:
        x, y = inx[0] + coord[0], inx[1] + coord[1]
        b[x][y] = 1


for i in range(n):
    a[i] = map(int, raw_input().split())

b = [[0] * m for i in range(n)]

for i in range(n - 1):
    for j in range(m - 1):
        if a[i][j]:
            if check((i, j,)):
                ans.append((i, j,))
can = True
# print ans
for i in ans:
    do(i)
    # print b
for i in range(n):
    for j in range(m):
        if a[i][j] != b[i][j]:
            can = False
if can:
    print len(ans)
    for i in ans:
        print i[0] + 1, i[1] + 1
else:
    print -1
# 3 3
# 1 1 1
# 1 1 1
# 0 1 1