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} 
import decimal,math
from collections import Counter,defaultdict
from fractions import gcd
from bisect import bisect_right,bisect_left
decimal.getcontext().prec = 15
def primeFactors(n): 
	arr=[]
	while n % 2 == 0: 
		arr.append(2) 
		n = n / 2
	for i in range(3,int(math.sqrt(n))+1,2): 
		while n % i== 0: 
			arr.append(i) 
			n = n / i 
	if n > 2: 
		arr.append(n)
		# print n
	return arr	 
def z_advanced(s):
	Z = [0] * len(s)
	Z[0] = len(s) 
	rt = 0
	lt = 0
	for k in range(1, len(s)):
		if k > rt:
			n = 0
			while n + k < len(s) and s[n] == s[n+k]:
				n += 1
			Z[k] = n
			if n > 0:
				lt = k
				rt = k+n-1
		else:
			p = k - lt  # Pair index.
			right_part_len = rt - k + 1 
			if Z[p] < right_part_len:
				Z[k] = Z[p]
			else:
				i = rt + 1
				while i < len(s) and s[i] == s[i - k]:
					i += 1
				Z[k] = i - k
 
				lt = k
				rt = i - 1
	return max(Z)

n,m = map(int,raw_input().split())
a=[]
b=[]
for k in range(n):
	a1 = map(int,raw_input().split())
	a.append(a1)
	p=[0]*m
	b.append(p)
ans=[]
# print a
# print b	
for i in range(n):
	for j in range(m):
		if (i+1)<n	and j+1<m :
			if(a[i][j]==1 and a[i][j+1]==1 and a[i+1][j]==1 and a[i+1][j+1]==1):
				b[i][j]=1
				b[i][j+1]=1
				b[i+1][j+1]=1
				b[i+1][j]=1

				ans.append((i+1,j+1))
				# print ans
				# print b
flag=0
for i in range(n):
	for j in range(m):
		if(b[i][j]!=a[i][j]):
			print -1
			exit()
print len(ans)
for i in range(len(ans)):
	print ans[i][0],ans[i][1]