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 io, sys, atexit, os
import math as ma
from sys import exit
from decimal import Decimal as dec
from itertools import permutations
from itertools import combinations


def li ():
	return list (map (int, input ().split ()))


def num ():
	return map (int, input ().split ())


def nu ():
	return int (input ())


def find_gcd ( x, y ):
	while (y):
		x, y = y, x % y
	return x


def lcm ( x, y ):
	gg = find_gcd (x, y)
	return (x * y // gg)


mm = 1000000007
yp = 0

def solve ():
	t = 1
	for tt in range (t):
		n,m=num()
		a=[0]*n
		xx=[]
		fl=True
		b=[0]*n
		for i in range(n):
			a[i]=li()
			b[i]=[0]*m
		for i in range(n-1):
			for j in 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):
					xx.append((i,j))
					b [ i ] [ j ] = 1
					b [ i ] [ j + 1 ] = 1
					b [ i + 1 ] [ j ] = 1
					b [ i + 1 ] [ j + 1 ] = 1
		for i in range(n):
			for j in range(m):
				if(a[i][j]!=b[i][j]):
					fl=False
		if(fl):
			print(len(xx))
			for i in range(len(xx)):
				print(xx[i][0]+1,xx[i][1]+1)
		else:
			print(-1)







if __name__ == "__main__":
	solve ()