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.io.*;
import java.util.*;

public class GFG 
{
    public static void main (String[] args) 
    {
	    Scanner sc=new Scanner(System.in);
	    int n=sc.nextInt();
	    int m=sc.nextInt();
	    int ar[][]=new int[n+2][m+2];
	    for(int i=1;i<n+1;i++)
	    {
	        for(int j=1;j<m+1;j++)
	        {
	            ar[i][j]=sc.nextInt();
	        }
	    }
	    int flag=0;
	    int ans=0;
	    int as[][]=new int[2500][2];
	    for(int i=1;i<=n;i++)
	    {
	        for(int j=1;j<=m;j++)
	        {
	            if(ar[i][j]==1)
	            {
	                if(ar[i][j+1]==1&&ar[i+1][j+1]==1&&ar[i+1][j]==1)
	                {
	                    as[ans][0]=i;
	                    as[ans][1]=j;
	                    ans++;
	                }
	                else if(ar[i][j+1]==1&&ar[i-1][j+1]==1&&ar[i-1][j]==1)
	                {
	                    continue;
	                }
	                else if(ar[i][j-1]==1&&ar[i-1][j-1]==1&&ar[i-1][j]==1)
	                {
	                    continue;
	                }
	                else if(ar[i][j-1]==1&&ar[i+1][j-1]==1&&ar[i+1][j]==1)
	                {
	                    continue;
	                }
	                else
	                {
	                    flag=1;
	                    break;
	                }
	            }
	        }
	        if(flag==1)
	        {
	            break;
            }
	    }
	    if(flag==1)
	        {
	            System.out.println("-1");
	        }
	        else
	        {
	            System.out.println(ans);
	            for(int i=0;i<ans;i++)
	            {
	                System.out.println(as[i][0]+" "+as[i][1]);
	            }
	        }
	}
}