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.*;
import java.util.*;

public class b_square {

	static int[][] matrix;
	static int[][] check;
	
	public static void main(String[] args) throws Exception {
		BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
		StringTokenizer st1 = new StringTokenizer(br.readLine(), " ");
		BufferedWriter bw = new BufferedWriter(new OutputStreamWriter(System.out));
		int n = Integer.parseInt(st1.nextToken());
		int m = Integer.parseInt(st1.nextToken());
		matrix = new int[n + 1][m + 1];
		check = new int[n+1][m+1];
		if (n < 2 || m > 50) {
			System.out.println("-1");
			return;
		}
		for (int i = 0; i < n; i++) {
			StringTokenizer st2 = new StringTokenizer(br.readLine(), " ");
			for (int j = 0; j < m; j++) {
				matrix[i][j] = Integer.parseInt(st2.nextToken());
				check[i][j] = 0;
			}
		}
		ArrayList<String> sol = new ArrayList<>();
		for (int i = 0; i < n; i++) {
			for (int j = 0; j < m; j++) {
				if(matrix[i][j]==1&&matrix[i][j+1]==1&&matrix[i+1][j]==1&&matrix[i+1][j+1]==1) {
					sol.add((i+1)+" " + (j+1));
					check[i][j]=check[i+1][j]=check[i][j+1]=check[i+1][j+1]=1;
				}
			}
		}
		
		for(int i=0; i<n; i++) {
			for(int j=0; j<m; j++) {
				if(check[i][j] != matrix[i][j]) {
					bw.write("-1");
					bw.flush();
					return;
				}
			}
		}
		bw.write(sol.size()+"\n");
		for(int i=0; i<sol.size(); i++) {
			bw.write(sol.get(i)+"\n");
		}
		
		bw.flush();
		bw.close();
	}
}