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} 
//Square Filling
import java.io.BufferedReader;
import java.io.InputStreamReader;
import java.io.IOException;
import java.util.StringTokenizer;
public class SquareFilling
{
	public static void main(String args[]) throws IOException
	{
		BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
		StringTokenizer st = new StringTokenizer(br.readLine());
		int n = Integer.parseInt(st.nextToken());
		int m = Integer.parseInt(st.nextToken());
		int a[][] = new int[n][m];
		int b[][] = new int[n][m];
		boolean flag = false;
		for(int i = 0; i < n; i++)
		{
			st = new StringTokenizer(br.readLine());
			for(int j = 0; j < m; j++)
			{
				a[i][j] = Integer.parseInt(st.nextToken());
				if(a[i][j] != 0)
					flag = true;
			}
		}
		if(!flag)
		{
			System.out.println("0");
			return;
		}
		StringBuilder ans = new StringBuilder();
		int count = 0;
		for(int i = 0; i < n-1; i++)
		{
			for(int j = 0; j < m-1; j++)
			{
				if(a[i][j] == 1 && a[i][j+1] == 1 && a[i+1][j] == 1 && a[i+1][j+1] == 1)
				{
					count++;
					b[i][j] = 1;
					b[i][j+1] = 1;
					b[i+1][j] = 1;
					b[i+1][j+1] = 1;
					ans.append(Integer.toString(i+1)+" "+Integer.toString(j+1)+"\n");
				}
				if(a[i][j] != b[i][j])
				{
					flag = false;
					break;
				}
			}
			if(!flag)
				break;
		}
		if(flag)
		{
			for(int i = n-1; i < n; i++)
			{
				for(int j = 0; j < m; j++)
				{
					if(a[i][j] != b[i][j])
					{
						flag = false;
						break;
					}
				}
				if(!flag)
					break;
			}
			for(int i = 0; i < n; i++)
			{
				for(int j = m-1; j < m; j++)
				{
					if(a[i][j] != b[i][j])
					{
						flag = false;
						break;
					}
				}
				if(!flag)
					break;
			}
		}
		if(count == 0 || !flag)
			System.out.println("-1");
		else
		{
			System.out.println(count);
			System.out.println(ans);
		}
	}
}