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.io.PrintWriter;
import java.util.ArrayList;
import java.util.List;
import java.util.Random;
import java.util.Scanner;

public class TaskA {

	static Scanner in = new Scanner(System.in);
	static PrintWriter w = new PrintWriter(System.out);

	public static void main(String[] args) {
//		int t = Integer.parseInt(in.nextLine());
//		outer: while (t-- > 0) {
//
//		}
		int n = in.nextInt();
		int m = in.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] = in.nextInt();
		int count = 0;
		List<Integer> x = new ArrayList<>();
		List<Integer> y = new ArrayList<>();
		for(int i = 0; i<n; i++) {
			for(int j = 0; j<m; j++) {
				if(i>0 && j>0 && a[i][j] == 1 && a[i-1][j] == 1  && a[i][j-1] == 1 && a[i-1][j-1] == 1) {
					count++;
					x.add(i);
					y.add(j);
					b[i][j] = 1;
					b[i][j-1] = 1;
					b[i-1][j] = 1;
					b[i-1][j-1] = 1;
				}
			}
		}
		boolean flag = true;
		for(int i = 0; i<n; i++) {
			for(int j = 0; j<m; j++) {
				if(a[i][j] != b[i][j])
					flag = false;
			}
		}
		if(!flag)
			w.println(-1);
		else {
			w.println(count);
			for(int i = 0; i<count; i++) {
				w.println(x.get(i) + " " + y.get(i));
			}
		}
		w.flush();
		w.close();
	}

	private static int solve(int n) {

		return -1;
	}

	private static void shuffleArray(int[] arr) {
		int n = arr.length;
		Random rnd = new Random();
		for (int i = 0; i < n; ++i) {
			int tmp = arr[i];
			int randomPos = rnd.nextInt(n);
			arr[i] = arr[randomPos];
			arr[randomPos] = tmp;
		}
	}

	private static void shuffleArray(long[] arr) {
		int n = arr.length;
		Random rnd = new Random();
		for (int i = 0; i < n; ++i) {
			long tmp = arr[i];
			int randomPos = i + rnd.nextInt(n - i);
			arr[i] = arr[randomPos];
			arr[randomPos] = tmp;
		}
	}
}