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 java.util.*;

public class codeforce {
	
	static boolean ch(char [][] a,char [][] b,int n,int m)
	{int i,j;
		
		for(i=0;i<n;i++)
		{
			for(j=0;j<m;j++)
			{
				if(a[i][j]!=b[i][j])
					return false;
			}
		}
		
		return true;
		
		
	}
public static void main(String[] args) {
	Scanner scan=new Scanner(System.in);

	int n=scan.nextInt();
	int m=scan.nextInt();
	
	int i,j;
	char [][] a=new char [n][m];
	char [][] b=new char[n][m];
	
	for(i=0;i<n;i++)
	{
		for(j=0;j<m;j++)
		{
			a[i][j]=scan.next().charAt(0);
		b[i][j]='0';	
			
		}
	}

			
	ArrayList<Integer>la=new ArrayList<Integer>();
	ArrayList<Integer>r=new ArrayList<Integer>();
	
	for(i=0;i<n-1;i++)
	{
		for(j=0;j<m-1;j++)
		{
			if(a[i][j]=='1'&&a[i][j+1]=='1'&&a[i+1][j]=='1'&&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';
				
				la.add(i+1);
				r.add(j+1);
			}
			
			
		}
	}
	
	if(ch(a,b,n,m))
	{
		System.out.println(la.size());
		
		for(i=0;i<la.size();i++)
		{
			System.out.println(la.get(i)+" "+r.get(i));
		}
	}
	else
	{
		System.out.println("-1");
		
	}
	
	
	
}
}
