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 = list(map(int,input().split(" ")))
matrix = []
line = []

def convert(i,j,mat):
	#print(mat)
	for p in range(i,i+2):
		for q in range(j,j+2):
			mat[p][q] = 1
			#print(mat[p][q])
	#print(mat)
	return mat

def check(i,j,mat):
	for p in range(i,i+2):
		for q in range(j,j+2):
			if(mat[p][q] == 0):
				return False
	return True
for i in range(n_m[0]):
	line = list(map(int,input().split(" ")))
	matrix.append(line)

prop_matrix = []
for i in range(n_m[0]):
	prop_matrix.append(matrix[i][:])

for i in range(n_m[0]):
	for j in range(n_m[1]):
		prop_matrix[i][j] = 0

steps = []
for i in range(n_m[0]-1):
	for j in range(n_m[1]-1):
		if(check(i,j,matrix)):
			#print(prop_matrix)
			prop_matrix = convert(i,j,prop_matrix)
			#print(prop_matrix)
			steps.append([i,j])

def final_check(mat1,mat2,size):
	for i in range(size[0]):
		for j in range(size[1]):
			if(mat1[i][j]!=mat2[i][j]):
				return False
	return True

#print(prop_matrix)
#print(matrix)
if(final_check(prop_matrix,matrix,n_m)):
	print(len(steps))
	for i in steps:
		print(str(i[0]+1) + " " + str(i[1]+1))
else:
	print(-1)   
