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 Solution
{
	public static void main(String[] args)
	{
		Scanner in=new Scanner(System.in);
		int n=in.nextInt();
		int m=in.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]=in.nextInt();
		}
		ArrayList<Integer> x=new ArrayList<Integer>();
		ArrayList<Integer> y=new ArrayList<Integer>();
		for(int i=0;i<n;i++)
		{
			for(int j=0;j<m;j++)
			{
				if(a[i][j]==1)
				{
					boolean f2,f3,f4;
					f2=f3=f4=false;
					if(j+1<m && a[i][j+1]==1)
						f2=true;
					if(i+1<n && a[i+1][j]==1)
						f3=true;
					if((i+1<n && j+1<m) && a[i+1][j+1]==1)
						f4=true;
					if(f2 && f3 && f4)
					{
						x.add(i);
						y.add(j);
					}
				}
			}
		}
		for(int i=0;i<x.size();i++)
		{
			int X=x.get(i);
			int Y=y.get(i);
			b[X][Y]=1;
			b[X+1][Y]=1;
			b[X][Y+1]=1;
			b[X+1][Y+1]=1;
		}
		for(int i=0;i<n;i++)
		{
			for(int j=0;j<m;j++)
			{
				if(a[i][j]!=b[i][j])
				{
					System.out.println(-1);
					return;
				}
			}
		}
		System.out.println(x.size());
		for(int i=0;i<x.size();i++)
			System.out.println((x.get(i)+1)+" "+(y.get(i)+1));
	}
}
