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.BufferedReader;
import java.io.InputStreamReader;
import java.util.Arrays;

public class question1
{
	
	public static void main(String[] args) throws Exception, Exception {
		InputStreamReader is = new InputStreamReader(System.in);
		BufferedReader br = new BufferedReader(is);
		String ab[] = br.readLine().split(" ");
		int n = Integer.parseInt(ab[0]);
		int m = Integer.parseInt(ab[1]);
		String arr[][] = new String[n][];
		for(int i = 0;i<n;i++) {
			arr[i] = br.readLine().split(" ");
		}
		int[][] ans = new int[n][m];
		int ans2[][] = new int[n*m][2];
		int index = 0;
		for(int i =0;i<n-1;i++) {
			for(int j =0;j<m-1;j++) {
				if(arr[i][j].equals("1") && arr[i+1][j].equals("1") && arr[i][j+1].equals("1") && arr[i+1][j+1].equals("1")) {
					ans[i][j] = 1;
					ans[i+1][j] = 1;
					ans[i+1][j+1] = 1;
					ans[i][j+1]= 1;
					ans2[index][0] = i;
					ans2[index][1] = j;
					index++;
				}
				
			}
		}
		int flag = 0;
		
		for(int i =0;i<n;i++) {
			for(int j =0;j<m;j++) {
				if(Integer.parseInt(arr[i][j])!=ans[i][j]) {
					flag = 1;
					break;
				}
			}
		}
		if(flag==1) {
			System.out.println(-1);
		}else {
			System.out.println(index);
			for(int i =0;i<index;i++) {
				System.out.println((ans2[i][0]+1)+" "+(ans2[i][1]+1));
			}
		}
	}
}
