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.lang.*;
import java.io.*;

public class Main
{
	public static void main (String[] args) throws java.lang.Exception
	{
		InputStream inputStream = System.in;
		OutputStream outputStream = System.out;
		InputReader in = new InputReader(inputStream);
		PrintWriter out = new PrintWriter(outputStream);
		TaskB solver = new TaskB();
		solver.solve(1, in, out);
		
		out.close();
	}
	
	static class TaskB
	{
		int[][] a = new int[55][55];
		int[][] b = new int[55][55];
		
		void solve(int TestNumber, InputReader in, PrintWriter out)
		{
			int n = in.nextInt();
			int m = in.nextInt();
			
			for(int i = 1; i <= n; i++)
				for(int j = 1; j <= m; j++)
					a[i][j] = in.nextInt();
					
			int ans = 0;
			for(int i = 1; i < n; i++)
			{
				for(int j = 1; j < m; j++)
				{
					if(a[i][j] + a[i + 1][j] + a[i][j + 1] + a[i + 1][j + 1] == 4)
					{
						b[i][j] = 1;
						b[i + 1][j] = 1;
						b[i][j + 1] = 1;
						b[i + 1][j + 1] = 1;
						ans++;
					}
				}
			}
			
			for(int i = 1; i <= n; i++)
				for(int j  = 1; j <= m; j++)
					if((a[i][j] ^ b[i][j]) == 1)
					{
						out.println("-1");
						return;
					}
			
			out.println(ans);
			for(int i = 1; i < n; i++)
			{
				for(int j = 1; j < m; j++)
				{
					if(a[i][j] + a[i + 1][j] + a[i][j + 1] + a[i + 1][j + 1] == 4)
					{
						out.println(i + " " + j);
					}
				}
			}
		}
	}
	
	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());
		}
	}
}