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 A
{
    public static class Pair
    {
        int f;
        int s;
    }
    public static void main(String args[])
    {
        Scanner sc=new Scanner(System.in);
        int n=sc.nextInt();
        int m=sc.nextInt();
        int a[][]=new int[n][m];
        for(int i=0;i<n;i++)
        {
            for(int j=0;j<m;j++)
            {
                a[i][j]=sc.nextInt();
            }
        }
        ArrayList<Pair> arr=new ArrayList<>();
        int count=0;
        int b[][]=new int[n][m];
        for(int i=0;i<n-1;i++)
        {
            for(int j=0;j<m-1;j++)
            {
                if(a[i][j]==1&&a[i][j+1]==1&&a[i+1][j]==1&&a[i+1][j+1]==1)
                {
                    b[i][j]=1;
                    b[i][j+1]=1;
                    b[i+1][j]=1;
                    b[i+1][j+1]=1;
                    Pair p=new Pair();
                    p.f=i+1;
                    p.s=j+1;
                    arr.add(p);
                }
                /*else if(a[i][j]==0&&a[i][j+1]==0&&a[i+1][j]==0&&a[i+1][j+1]==0)
                {
                    count++;
                }*/
                
            }
        }
        int flag=0;
        for(int i=0;i<n;i++)
        {
            for(int j=0;j<m;j++)
            {
                if(a[i][j]!=b[i][j])
                {
                    flag=1;
                    break;
                }
            }
        }
        if(flag==1)
        System.out.println(-1);
        else
        {
            System.out.println(arr.size());
            for(int i=0;i<arr.size();i++)
            {
                System.out.println(arr.get(i).f+" "+arr.get(i).s);
            }
        }
    }
}