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.List;
import java.util.Scanner;
import java.util.ArrayList;

/**
 * Built using CHelper plug-in
 * Actual solution is at the top
 *
 * @author Sanket Makani
 */
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);
        BSquareFilling solver = new BSquareFilling();
        solver.solve(1, in, out);
        out.close();
    }

    static class BSquareFilling {
        public void solve(int testNumber, Scanner in, PrintWriter out) {
            int n = in.nextInt();
            int m = in.nextInt();

            int arr[][] = new int[n][m];

            for (int i = 0; i < n; i++) {
                for (int j = 0; j < m; j++) {
                    arr[i][j] = in.nextInt();
                }
            }

            List<Integer> x = new ArrayList<>();
            List<Integer> y = new ArrayList<>();
            int result[][] = new int[n][m];

            for (int i = 0; i < n - 1; i++) {
                for (int j = 0; j < m - 1; j++) {
                    if (arr[i][j] == 1 && arr[i + 1][j] == 1 && arr[i][j + 1] == 1 && arr[i + 1][j + 1] == 1) {
                        x.add(i + 1);
                        y.add(j + 1);

                        result[i][j] = 1;
                        result[i + 1][j] = 1;
                        result[i][j + 1] = 1;
                        result[i + 1][j + 1] = 1;
                    }
                }
            }


            boolean isPossible = true;

            for (int i = 0; i < n; i++) {
                for (int j = 0; j < m; j++) {
                    isPossible &= result[i][j] == arr[i][j];
                }
            }

            if (isPossible) {
                out.println(x.size());
                for (int i = 0; i < x.size(); i++) {
                    out.println(x.get(i) + " " + y.get(i));
                }
            } else {
                out.println("-1");
            }
        }

    }
}

