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.io.IOException;
import java.util.ArrayList;
import java.util.Scanner;
 
public class Burgers{
	
	boolean[] used;
	
	public static void main(String[] args) throws IOException
	{
		new Burgers().run();
	}
 
	public void run() throws IOException
	{
		Scanner file = new Scanner(System.in);
		int N = file.nextInt();
		int M = file.nextInt();
		int[][] ints = new int[N][M];
		int[][] ans = new int[N][M];
		for(int i = 0;i<N;i++)
			for(int j = 0;j<M;j++)
				ints[i][j] = file.nextInt();
		ArrayList<String> answer = new ArrayList<String>();
		for(int i = 0;i<ints.length - 1;i++)
			for(int j = 0;j<ints[i].length - 1;j++)
			{
				if(ints[i][j] == 1 && ints[i][j+1]==1 && ints[i+1][j] == 1 && ints[i+1][j+1]==1)
				{
					answer.add(i+1+" "+(j+1));
					ans[i][j] = ans[i+1][j] = ans[i][j+1] = ans[i+1][j+1] = 1;
				}
			}
		boolean same = true;
		for(int i =0;i<ans.length;i++)
			for(int j = 0;j<ans[i].length;j++)
				if(ans[i][j] != ints[i][j])
					same = false;
		if(!same)
			System.out.println(-1);
		else {
			System.out.println(answer.size());
			for(String s:answer)
			{
				System.out.println(s);
			}
		}
	}
}