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 Main {
	public static void main(String args[])
	{
		Scanner sc=new Scanner(System.in);
		int n=sc.nextInt(),m=sc.nextInt(),ans=-1;
		ArrayList<data> list=new ArrayList<data>();
		int A[][]=new int[n][m],B[][]=new int[n][m];
		
		for(int i=0;i<n;i++)
			for(int j=0;j<m;j++)
				A[i][j]=sc.nextInt();
		for(int i=0;i<n-1;i++)
			for(int j=0;j<m-1;j++)
			{
				if(A[i][j]==1)
				{
					if(A[i][j+1]==0||A[i+1][j]==0||A[i+1][j+1]==0)
						continue;
					if((A[i][j]==1&&B[i][j]==0)||(A[i][j+1]==1&&B[i][j+1]==0)||(A[i+1][j]==1&&B[i+1][j]==0)||(A[i+1][j+1]==1&&B[i+1][j+1]==0))
					list.add(new data(i+1,j+1));
					B[i][j]=1;
					B[i][j+1]=1;
					B[i+1][j]=1;
					B[i+1][j+1]=1;
				}
			}
//		for(int i=0;i<n-1;i++)
//			if(A[i][m-1]==1&&B[i][m-1]==0)
//			{
//				if(A[i][m-2]==0||A[i+1][m-1]==0||A[i+1][m-2]==0)
//					continue;
//				list.add(new data(i+1,m-1));
//				B[i][m-1]=1;
//				B[i][m-2]=1;
//				B[i+1][m-1]=1;
//				B[i+1][m-2]=1;
//			}
//		for(int i=0;i<m-1;i++)
//		{
//			if(A[n-1][i]==1&&B[n-1][i]==0)
//			{
//				if(A[n-2][i]==0||A[n-2][i+1]==0||A[n-1][i+1]==0)
//					continue;
//				list.add(new data(n-1,i+1));
//				B[n-1][i]=1;
//				B[n-2][i]=1;
//				B[n-2][i+1]=1;
//				B[n-1][i+1]=1;
//			}
//		}
//		if(A[n-1][m-1]==1&&B[n-1][m-1]==0)
//		{
//			if(A[n-2][m-2]==0||A[n-2][m-1]==0||A[n-1][m-2]==0||A[n-1][m-1]==0)
//				{}
//			else
//			{
//			list.add(new data(n-1,m-1));
//			B[n-2][m-2]=1;
//			B[n-2][m-1]=1;
//			B[n-1][m-2]=1;
//			B[n-1][m-1]=1;
//			}
//		}
		boolean bool=true;
		for(int i=0;i<n&&bool;i++)
			for(int j=0;j<m&&bool;j++)
				if(A[i][j]!=B[i][j])
				{
					bool=false;
				}
		
		if(!bool)
			System.out.println(-1);
		else
		{
			System.out.println(list.size());
			for(int i=0;i<list.size();i++)
			{
				data now=list.get(i);
				System.out.println(now.x+" "+now.y);
			}
		}
	}

}
class data
{
	int x,y;
	data(){}
	data(int a,int b)
	{
		x=a;y=b;
	}
}