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.ArrayList;
import java.util.Scanner;
public class SquareFilling {

	public static void main(String[] args) {
		Scanner obj=new Scanner(System.in);
		int n=obj.nextInt();
		int m=obj.nextInt();
		int[][] a=new int[n][m];
		int[][] b=new int[n][m];
		int sa=0,sb=0;
		String c="";
		ArrayList<Integer> arr=new ArrayList<>();

		for(int i=0;i<n;i++)
		{
			for(int j=0;j<m;j++)
			{
				a[i][j]=obj.nextInt();
				if(a[i][j]==1)
				sa++;
				b[i][j]=0;


			}
		}
		int k=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]=1;
					b[i+1][j]=1;
					b[i][j+1]=1;
					b[i+1][j+1]=1;
					arr.add(i+1);
					arr.add(j+1);
					k++;

				}
			}
		}
		for(int i=0;i<n;i++)
		{
			for(int j=0;j<m;j++)
			{
				if(b[i][j]==1)
				{
					sb++;
				}
			}
		}
		//System.out.println(arr);
		if(sa==sb)
		{
			System.out.println(k);
			for(int i=0;i<arr.size();i++)
			{
				if(i%2==0)
				System.out.print(arr.get(i)+" "+arr.get(i+1));
				else
					System.out.println();
			}
		}

		else
			System.out.println("-1");
	}
}


