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} 
from collections import Counter as C,defaultdict as D,deque as Q
from operator import itemgetter as I
from itertools import product as P
from bisect import bisect_left as BL,bisect_right as BR
from heapq import heappush as HPUSH,heappop as HPOP
from math import floor as MF,ceil as MC, gcd as MG,factorial as F,sqrt as SQRT, inf as INFINITY,log as LOG
from sys import stdin, stdout
INPUT=stdin.readline
PRINT=stdout.write

def player1():
	print("")

def player2():
	print("")

def isPrime(n):

	for i in range(2,MC(SQRT(n))+1):
		if n%i==0:
			return False
	return True

def factors(x):

	ans=[]

	for i in range(1,MC(SQRT(x))+1):
		if x%i==0:
			ans.append(i)
			if x%(x//i)==0:
				ans.append(x//i)
	return ans
def checkPath(source,destination,g):
	visited=[0]*101
	q=Q()
	q.append(source)
	visited[source]=1
	while q:
		node=q.popleft()
		if node==destination:
			return 1
		for v in g[node]:
			if not visited[v]:
				q.append(v)
				visited[v]=1
	return 0
def main():

	#for _ in range(int(INPUT())):

	n,m=map(int,INPUT().split( ))
	a=[]
	for i in range(n):
		a.append([*map(int,INPUT().split( ))])
	b=[[0 for i in range(m)]for j in range(n)]

	ans=[]
	for i,j in P(range(n-1),range(m-1)):
		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;b[i+1][j+1]=1
			ans.append((i+1,j+1))
	for i,j in P(range(n),range(m)):
		if a[i][j]!=b[i][j]:
			break
	else:
		PRINT("%d\n"%(len(ans)))
		for x,y in ans:
			PRINT("%d %d\n"%(x,y))
		return
	PRINT("%d\n"%(-1))

main()