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.lang.*;

public class solution{
    
    public static void main(String args[]){
        
        Scanner scan = new Scanner(System.in);
        int n = scan.nextInt();
        int m = scan.nextInt();
        
        int a[][] = new int[n][m];
        int b[][] = new int[n][m];
        
        for(int i=0; i<n; i++){
            for(int j=0; j<m; j++){
                a[i][j] = scan.nextInt();
            }
        }
        ArrayList<String> arr = new ArrayList<>();
        int count = 0;
        for(int i=0; i<n-1; i++){
            for(int j=0; j<m-1; j++){
                if(a[i][j] == 1 && a[i+1][j] == 1 && a[i][j+1] == 1 && a[i+1][j+1] == 1)
                {    b[i][j] = b[i+1][j] = b[i][j+1] = b[i+1][j+1] = 1;
                     arr.add(Integer.toString(i+1)+" "+Integer.toString(j+1));
                     count++;}
            }
        }
        
        for(int i=0; i<n; i++){
            for(int j=0; j<m; j++){
                if(a[i][j] !=  b[i][j]){
                    count = -1; break;
                }
            }
        }
        
        if(count > 0){
            System.out.println(count);
            for(int i=0; i<arr.size(); i++){
                String s[] = arr.get(i).trim().split(" ");
                System.out.println(s[0] + " " + s[1]);    
            }
        }else
            System.out.println(count);
    }
}