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.OutputStream;
import java.io.IOException;
import java.io.InputStream;
import java.io.PrintWriter;
import java.util.Scanner;

/**
 * Built using CHelper plug-in
 * Actual solution is at the top
 */
public class Main
{
    public static void main(String[] args)
    {
        InputStream inputStream = System.in;
        OutputStream outputStream = System.out;
        Scanner in = new Scanner(inputStream);
        PrintWriter out = new PrintWriter(outputStream);
        TaskB solver = new TaskB();
        solver.solve(1, in, out);
        out.close();
    }

    static class TaskB
    {
        public void solve(int testNumber, Scanner in, PrintWriter out)
        {
            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();
                }
            }
            boolean good = true;
            int op = 0;
            StringBuilder stringBuilder = new StringBuilder();
            outerloop:
            for (int i = 0; i < n; i++)
            {
                for (int j = 0; j < m; j++)
                {
                    if (a[i][j] != b[i][j])
                    {
                        if (a[i][j] == 0)
                        {
                            good = false;
                            break outerloop;
                        } else
                        {
                            //too bottom and right
                            if (canPaint(a, b, i - 1, j - 1, n, m))
                            {
                                b[i - 1][j - 1] = 1;
                                b[i - 1][j] = 1;
                                b[i][j - 1] = 1;
                                b[i][j] = 1;
                                op++;
                                stringBuilder.append(i);
                                stringBuilder.append(" ");
                                stringBuilder.append(j);
                                stringBuilder.append("\n");
                                //too right
                            } else if (canPaint(a, b, i, j - 1, n, m))
                            {
                                b[i][j - 1] = 1;
                                b[i + 1][j - 1] = 1;
                                b[i][j] = 1;
                                b[i + 1][j] = 1;
                                op++;
                                stringBuilder.append(i + 1);
                                stringBuilder.append(" ");
                                stringBuilder.append(j);
                                stringBuilder.append("\n");
                                //too bottom
                            } else if (canPaint(a, b, i - 1, j, n, m))
                            {
                                b[i - 1][j] = 1;
                                b[i][j] = 1;
                                b[i - 1][j + 1] = 1;
                                b[i][j + 1] = 1;
                                op++;
                                stringBuilder.append(i);
                                stringBuilder.append(" ");
                                stringBuilder.append(j + 1);
                                stringBuilder.append("\n");
                            } else if (canPaint(a, b, i, j, n, m))
                            {
                                //base case
                                b[i][j] = 1;
                                b[i + 1][j] = 1;
                                b[i][j + 1] = 1;
                                b[i + 1][j + 1] = 1;
                                op++;
                                stringBuilder.append(i + 1);
                                stringBuilder.append(" ");
                                stringBuilder.append(j + 1);
                                stringBuilder.append("\n");
                            }
                        }
                    }
                }
            }
            outerloop2:
            for (int i = 0; i < n; i++)
            {
                for (int j = 0; j < m; j++)
                {
                    if (a[i][j] != b[i][j])
                    {
                        good = false;
                        break outerloop2;
                    }
                }
            }

            if (!good)
                out.print("-1");
            else
            {
                out.println(op);
                out.println(stringBuilder.toString());
            }
        }

        static boolean canPaint(int a[][], int b[][], int i, int j, int n, int m)
        {
            if (i + 1 == n || j + 1 == m) return false;
            if (i < 0 || j < 0) return false;

            if ((a[i][j] == 1 && a[i + 1][j] == 1 && a[i][j + 1] == 1 && a[i + 1][j + 1] == 1) &&
                        (b[i][j] == 0 || b[i + 1][j] == 0 || b[i][j + 1] == 0 || b[i + 1][j + 1] == 0))
                return true;
            else
                return false;
        }

    }
}

