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.lang.Math;
import java.util.ArrayList;
import java.util.Scanner;
 
 
public class Codeforces1 {
 
    public static void makeOne(int[][] B,int i,int j)
    {
        B[i][j]=1;
        B[i][j+1]=1;
        B[i+1][j]=1;
        B[i+1][j+1]=1;
    }
     public static boolean isOne(int[][] B,int i,int j)
     {
         return (B[i][j]==1 && B[i][j+1]==1 && B[i+1][j]==1 && B[i+1][j+1]==1);
     }
    public static void main(String[] args) {
      
       Scanner scan=new Scanner(System.in);
       int n=scan.nextInt();
       int m=scan.nextInt();
       int i,j;
       int[][] A=new int[n][m];
       int[][] B=new int[n][m];
        ArrayList<Case> a=new ArrayList<Case>();
       int flag=0;
        
        for(i=0;i<n;i++)
        {
           scan.nextLine();
       
           for(j=0;j<m;j++)
           {   A[i][j]=scan.nextInt();
           if(A[i][j]!=0) flag=1;}
        }
        
        
        if (flag==0)
        {
            System.out.println(0);
            System.exit(0);
        }
                
        for(i=0;i<n-1;i++)
            for(j=0;j<m-1;j++)
            {
                if(isOne(A,i,j))
                {
                    makeOne(B,i,j);
                    
                    Case d=new Case();
                    d.i=i+1;
                    d.j=j+1;
                    a.add(d);
                }
            }
        
        for(i=0;i<n;i++)
            for(j=0;j<m;j++)
            {
                if(A[i][j] != B[i][j])
                {
                    System.out.println(-1);
                    System.exit(0);
                }
            }
        
        System.out.println(a.size());
        for(i=0;i<a.size();i++)
        {
            System.out.println(a.get(i).i+" "+a.get(i).j);
        }
    }
}
 
class Case
{
    int i,j;
}