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} 
/*input
 

2 4
1 1 1 1
1 1 1 1


 
 
*/
import java.io.*;
import java.util.*;
 
 
 
 
public class mymy
{
	
 
	static OutputStream outputStream = System.out;
	static PrintWriter out = new PrintWriter(outputStream);
	static InputStream inputStream = System.in;
	static InputReader br = new InputReader(inputStream);
 
 
	// static BufferedReader br;
	// static BufferedWriter out;

	
	
 
	public static void main(String[] args)throws IOException
	{
		// br=new BufferedReader(new FileReader("deposits.in"));


		int n=br.nextInt();
		int m=br.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]=br.nextInt();
		}

		ArrayList<Integer> l=new ArrayList<Integer>();
		ArrayList<Integer> r=new ArrayList<Integer>();


		for(int i=0;i<n-1;i+=2)
		{
			for(int j=0;j<m-1;j+=2)
			{
				if(a[i][j]==1 && a[i+1][j]==1 && a[i][j+1]==1 && a[i+1][j+1]==1)
				{
					if(b[i][j]==0 || b[i+1][j]==0 || b[i][j+1]==0 || b[i+1][j+1]==0)
					{
						l.add(i+1);
						r.add(j+1);
						b[i][j]=1;
						b[i+1][j]=1;
						b[i][j+1]=1;
						b[i+1][j+1]=1;
					}
				}
			}
		}

		for(int i=0;i<n-1;i+=1)
		{
			for(int j=0;j<m-1;j+=1)
			{
				if(a[i][j]==1 && a[i+1][j]==1 && a[i][j+1]==1 && a[i+1][j+1]==1)
				{
					if(b[i][j]==0 || b[i+1][j]==0 || b[i][j+1]==0 || b[i+1][j+1]==0)
					{
						l.add(i+1);
						r.add(j+1);
						b[i][j]=1;
						b[i+1][j]=1;
						b[i][j+1]=1;
						b[i+1][j+1]=1;
					}
				}
			}
		}



		int f=0;

		for(int i=0;i<n;i++) for(int j=0;j<m;j++) if(a[i][j]!=b[i][j]) f=1;

		if(f==1)
		{
			out.println(-1);
		}
		else
		{
			out.println(l.size());
			for(int i=0;i<l.size();i++) out.println(l.get(i)+" "+r.get(i));
		}


		
 
		out.close();
 
	}
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
	static class InputReader {
		public BufferedReader reader;
		public StringTokenizer tokenizer;
 
		public InputReader(InputStream stream) {
			reader = new BufferedReader(new InputStreamReader(stream), 32768);
			tokenizer = null;
		}
 
		public String next() {
			while (tokenizer == null || !tokenizer.hasMoreTokens()) {
				try {
					tokenizer = new StringTokenizer(reader.readLine());
				} catch (IOException e) {
					throw new RuntimeException(e);
				}
			}
			return tokenizer.nextToken();
		}
 
		public int nextInt() {
			return Integer.parseInt(next());
		}
		public long nextLong() {
			return Long.parseLong(next());
		}
 
	}
	
}