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} 
/* package whatever; // don't place package name! */
import java.util.*;
import java.lang.*;
import java.io.*;
 
/* Name of the class has to be "Main" only if the class is public. */
public class Ideone
{
	public static void main (String[] args) throws java.lang.Exception
	{
		// your code goes here
		BufferedReader br=new BufferedReader(new InputStreamReader(System.in));
		String[] s=br.readLine().split(" ");
		int n=Integer.parseInt(s[0]);
		int m=Integer.parseInt(s[1]);
		int[][] array=new int[n][m];
		for(int i=0;i<n;i++){
			s=br.readLine().split(" ");
			for(int j=0;j<m;j++){
				array[i][j]=Integer.parseInt(s[j]);
			}
		}
		int[][] copy=new int[n][m];
		for(int i=0;i<n;i++){
			for(int j=0;j<m;j++){
				copy[i][j]=0;
			}
		}
		List<int[]> al=new ArrayList<>();
		for(int i=0;i<(n-1);i++){
			for(int j=0;j<(m-1);j++){
				if(array[i][j]==1 && array[i][j+1]==1 && array[i+1][j]==1 && array[i+1][j+1]==1){
					al.add(new int[]{i+1,j+1});
					copy[i][j]=1;
					copy[i][j+1]=1;
					copy[i+1][j]=1;
					copy[i+1][j+1]=1;
				}
			}
		}
		for(int i=0;i<n;i++){
			for(int j=0;j<m;j++){
				if(array[i][j]!=copy[i][j]){
					System.out.println(-1);
					return;
				}
			}
		}
		System.out.println(al.size());
		for(int[] x:al){
			System.out.println(x[0]+" "+x[1]);
		}
	}
}