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.*;
public class Main {
    public static void main(String args[]) {
        // System.out.println("Hello World!");
        Scanner scn = new Scanner(System.in);
        int n = scn.nextInt();
        int m = scn.nextInt();

        int[][] arr = new int[n][m];
        for(int i=0;i<n;++i){
            for(int j=0;j<m;++j){
                arr[i][j] = scn.nextInt();
            }
        }

        boolean[][] work = new boolean[n][m];
        ArrayList<Integer> moves = new ArrayList<>();
        for(int i=0;i<n-1;++i){
            for(int j=0;j<m-1;++j){
                if(arr[i][j]==1 && arr[i][j+1]==1 && arr[i+1][j]==1 && arr[i+1][j+1]==1 && (!work[i][j]||!work[i+1][j]||!work[i][j+1]||!work[i+1][j+1])){
                    moves.add(i);
                    moves.add(j);
                    work[i][j]= true;
                    work[i][j+1] = true;
                    work[i+1][j+1] = true;
                    work[i+1][j]= true;
                }
            }
        }   

       

        boolean ans = true;

        for(int i=0;i<n;++i){
            for(int j=0;j<m;++j){
                if(arr[i][j]==1&&!work[i][j]){
                    ans = false;
                    break;
                }

            }
        }

        if(ans==false){
            System.out.println("-1");
        }else{
            System.out.println(moves.size()/2);
            for(int i=0;i<moves.size();i+=2){
                System.out.println((moves.get(i)+1)+" "+(moves.get(i+1)+1));
            }
        }


    }
}