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 cp {

	static class Pair{
		int a,b;
		Pair(int a,int b)
		{
			this.a=a;
			this.b=b;
		}
	}

    public static void main(String args[]) {

    	Scanner sc = new Scanner();

    		int r = sc.nextInt();
    		int c = sc.nextInt();


    		int ar[][] = new int[r][c];

    		for(int i=0;i<r;i++)
    		{
    			for(int j=0;j<c;j++)
    			{
    				ar[i][j] = sc.nextInt();
    			}
    		}

    		int res[][] = new int[r][c];

			ArrayList<Pair> al = new ArrayList<>();
    		
    		for(int i=0;i<r-1;i++)
    		{
    			for(int j=0;j<c-1;j++)
    			{
    				if(ar[i][j]==1 && ar[i+1][j]==1 && ar[i][j+1]==1 && ar[i+1][j+1]==1)
    				{
    					res[i][j]=1;
    					res[i+1][j]=1;
    					res[i][j+1]=1;
    					res[i+1][j+1]=1;
    					al.add(new Pair(i,j));
    					
    				}
    			}
    		}

			boolean poss = true;

    		for(int i=0;i<r;i++)
    		{
    			for(int j=0;j<c;j++)
    			{
    				if(ar[i][j]!=res[i][j])
    				{
    					poss = false;
    				}
    			}
    			if(!poss)
    				break;
    		}

    		if(poss)
    		{
    			out.println(al.size());

    			for(Pair p:al)
    				out.println((p.a+1)+" "+(p.b+1));
    		}else out.println("-1");
    		
    	out.close();
    }

    static	PrintWriter out=new PrintWriter(System.out);
	static class Scanner {
		BufferedReader br=new BufferedReader(new InputStreamReader(System.in));
		StringTokenizer st=new StringTokenizer("");
		String nextLine() {
			while (!st.hasMoreTokens())
				try { 
                                        st=new StringTokenizer(br.readLine());				               
                                } catch (IOException e) {}
			return st.nextToken();
		}
		char nextChar() {
			char c = '$';
				try { 
                                        c = (char)br.read();			               
                                } catch (IOException e) {}
			return c;
		}		
		int nextInt() {
			return Integer.parseInt(nextLine());
		}
		float nextFloat() {
			return Float.parseFloat(nextLine());
		}
		double nextDouble() {
			return Double.parseDouble(nextLine());
		}
		long nextLong() {
			return Long.parseLong(nextLine());
		}
	}
}