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
{
    PrintWriter out = new PrintWriter(new BufferedWriter(new OutputStreamWriter(System.out)));
    BufferedReader in = new BufferedReader(new InputStreamReader(System.in));

    public void go() throws IOException
    {
        StringTokenizer tok = new StringTokenizer(in.readLine());
        int n = Integer.parseInt(tok.nextToken());
        int m = Integer.parseInt(tok.nextToken());
        int[][] mat = new int[n][m];
        for (int i = 0; i < n; i++)
        {
            tok = new StringTokenizer(in.readLine());
            for (int e = 0; e < m; e++)
            {
                mat[i][e] = Integer.parseInt(tok.nextToken());
            }
        }
        ArrayList<int[]> moves = new ArrayList<>();
        int[][] mat2 = new int[n][m];
        for (int i = 0; i < n-1; i++)
        {
            for (int e = 0; e < m-1; e++)
            {
                if (mat[i][e] == 1 && mat[i+1][e] == 1 && mat[i][e+1] == 1 && mat[i+1][e+1] == 1)
                {
                    mat2[i][e] = 1;
                    mat2[i+1][e] = 1;
                    mat2[i][e+1] = 1;
                    mat2[i+1][e+1] = 1;
                    moves.add(new int[] {i+1, e+1});
                }
            }
        }
        boolean works = true;
        for (int i = 0; i < n; i++)
        {
            for (int e = 0; e < m; e++)
            {
                if (mat[i][e] != mat2[i][e])
                {
                    works = false;
                    break;
                }
            }
        }
        if (works)
        {
            out.println(moves.size());
            for (int[] mov : moves)
            {
                out.print(mov[0]);
                out.print(" ");
                out.println(mov[1]);
            }
        }
        else
        {
            out.println(-1);
        }

        out.flush();
        in.close();
    }

    public static void main(String[] args) throws IOException
    {
        new B().go();
    }
}
