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 Solution {
    
    public static void main(String[] args) throws Exception {
	//try{
	    BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
        OutputStream outputStream = System.out;
    	PrintWriter out = new PrintWriter(outputStream);

        int i, n, m, k=0, j;

        StringTokenizer st = new StringTokenizer(br.readLine());
	        n=Integer.parseInt(st.nextToken());
	        m=Integer.parseInt(st.nextToken());
	        
	        int[][] ar = new int[n][m];
	        int[][] b = new int[n][m];
	        
	        for(i=0;i<n;i++)
	        {
	            st = new StringTokenizer(br.readLine());
	            for(j=0;j<m;j++)
	            {
	                ar[i][j]=Integer.parseInt(st.nextToken());
	            }
	        }
	        
	        String str="";
	        
	        for(i=0;i<n-1;i++)
	        {
	            for(j=0;j<m-1;j++)
	            {
	                int c=0;
	                if(ar[i][j]==1)
	                {
	                    if(ar[i][j+1]==1)
	                        c++;
	                    if(ar[i+1][j]==1)
	                        c++;
	                    if(ar[i+1][j+1]==1)
	                        c++;
	                        
	               if(c==3)
	                {
	                    k++;
	                    str+=(i+1)+" "+(j+1)+"\n";
	                    b[i][j]=1;
	                    b[i][j+1]=1;
	                    b[i+1][j+1]=1;
	                    b[i+1][j]=1;
	                }
	                
	                }
	            }
	        }
	        int flag=0;
	        
	    for(i=0;i<n;i++)
	    {
	        if(!Arrays.equals(ar[i],b[i]))
	            {
	                out.print(-1);
	                flag=1;
	                break;
	            }
	    }
	    if(flag==0)
	        out.print(k+"\n"+str);
	out.flush();
	out.close();
	//}catch(Exception e){}
	}
}