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.*;
import java.io.*;

public class square2{
	public static void main(String[] args) throws IOException{
		BufferedReader br=new BufferedReader(new InputStreamReader(System.in));
		String a=br.readLine();
		String[] info=a.split(" ");
		int row=Integer.parseInt(info[0]);
		int col=Integer.parseInt(info[1]);
		int[][] grid=new int[row][col];
		for(int z=0; z<row; z++){
			a=br.readLine();
			info=a.split(" ");
			for(int p=0; p<col; p++)
				grid[z][p]=Integer.parseInt(info[p]);
		}
		ArrayList<Point> points=new ArrayList<Point>();
		for(int r=0; r<row-1; r++)
			for(int c=0; c<col-1; c++){
				int temp=grid[r][c]+grid[r][c+1]+grid[r+1][c]+grid[r+1][c+1];
				if(temp==4){
					points.add(new Point(r,c));
				}
			}
		int[][] blank=new int[row][col];
		for(int z=0; z<points.size(); z++){
			Point temp=points.get(z);
			int x=temp.x;
			int y=temp.y;
			blank[x][y]=1;
			blank[x+1][y]=1;
			blank[x][y+1]=1;
			blank[x+1][y+1]=1;
		}
		boolean poss=true;
		for(int r=0; r<row; r++)
			for(int c=0; c<col; c++)
				if(blank[r][c]!=grid[r][c])
					poss=false;
		if(poss){
			System.out.println(points.size());
			for (Point p: points){
				System.out.println((p.x+1)+" "+(p.y+1));
			}
		}
		else
			System.out.println(-1);
	}

}

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