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.*;
import java.io.*;
public class Main {
	public static void main(String args[]) throws java.lang.Exception	{
		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 arr[][] = new int[n][m];
        for (int i = 0; i < n ; i ++){
            s = br.readLine().split(" ");
            for (int j = 0; j < m ; j++)
                arr[i][j] = Integer.parseInt(s[j]);
        }
        boolean ans = modify(arr, n, m);
        if (!ans)System.out.println("-1");
	}
	
	public static boolean modify(int arr[][], int n, int m){
	    ArrayList<Integer> xs = new ArrayList<>();
	    ArrayList<Integer> ys = new ArrayList<>();
        int brr[][] = new int[n][m];
	    for (int i = 0; i < n ; i ++){
            for (int j = 0 ; j < m ; j ++){
                if (arr[i][j] == 1 && brr[i][j] == 0){
                    boolean found = false;
                    if (i-1 >= 0 && j-1 >= 0 && arr[i-1][j-1] ==1 && arr[i-1][j] == 1 && arr[i][j-1] == 1){
                        brr[i-1][j-1] = 1 ;
                        brr[i-1][j] = 1  ; 
                        brr[i][j-1] = 1;
                        brr[i][j] = 1;
                        found = true;
                        xs.add(i-1);
                        ys.add(j-1);
                    }
                    else if(i-1 >= 0 && j+1 < m && arr[i-1][j] == 1 && arr[i-1][j+1] == 1 && arr[i][j+1] == 1){
                        brr[i-1][j] = 1 ;
                        brr[i-1][j+1] = 1 ;
                        brr[i][j+1] = 1;
                        brr[i][j] = 1;
                        found = true;
                        xs.add(i-1);
                        ys.add(j);
                    }else if (j-1 >= 0 && i+1 < n && arr[i][j-1] ==1 && arr[i+1][j-1] == 1 && arr[i+1][j] == 1){
                        brr[i][j-1] = 1 ;
                        brr[i+1][j-1] = 1 ;
                        brr[i+1][j] = 1;
                        brr[i][j] = 1;
                        found = true;
                        xs.add(i);
                        ys.add(j-1);        
                    }
                    else if (i+1 < n && j+1 < m && arr[i][j+1] == 1 && arr[i+1][j] == 1 && arr[i+1][j+1] == 1){
                        brr[i][j+1] = 1 ;
                        brr[i+1][j] = 1 ;
                        brr[i+1][j+1] = 1;
                        found = true;
                        xs.add(i);
                        ys.add(j); 
                    }
                    else return false;
                }
            }
        }
        System.out.println(xs.size());
        for (int i = 0; i < xs.size(); i++)
            System.out.println((xs.get(i)+1)+" "+(ys.get(i)+1));
        return true;
	}
}