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.util.*;

public class B {
    public static void main(String[] args) {
        Scanner input = new Scanner(System.in);

        int n = input.nextInt();
        int m = input.nextInt();
        int[][] a = new int[n][m];
        int[][] b = new int[n][m];

        ArrayList<Pair> pairs = new ArrayList<>();

        for (int i = 0; i < n; i++) {
            for (int j = 0; j < m; j++) {
                a[i][j] = input.nextInt();
                b[i][j] = 0;
            }
        }

        for (int i = 0; i < n; i++) {
            for (int j = 0; j < m; j++) {
                if (a[i][j] == 1 && b[i][j] == 0) {
                    if (i + 1 < n && j + 1 < m && a[i][j] + a[i][j + 1] + a[i + 1][j] + a[i + 1][j + 1] == 4) {
                            b[i][j] = b[i][j + 1] = b[i + 1][j] = b[i + 1][j + 1] = 1;
                            pairs.add(new Pair(i + 1, j + 1));
                    } else if (i + 1 < n && j - 1 >= 0 && a[i][j] + a[i][j - 1] + a[i + 1][j] + a[i + 1][j - 1] == 4) {
                            b[i][j] = b[i][j - 1] = b[i + 1][j] = b[i + 1][j - 1] = 1;
                            pairs.add(new Pair(i + 1, j));
                    } else if (i - 1 >= 0 && j + 1 < m && a[i][j] + a[i][j + 1] + a[i - 1][j] + a[i - 1][j + 1] == 4) {
                            b[i][j] = b[i][j + 1] = b[i - 1][j] = b[i - 1][j + 1] = 1;
                            pairs.add(new Pair(i, j + 1));
                    } else if (i - 1 >= 0 && j - 1 >= 0 && a[i][j] + a[i][j - 1] + a[i - 1][j] + a[i - 1][j - 1] == 4) {
                            b[i][j] = b[i][j - 1] = b[i - 1][j] = b[i - 1][j - 1] = 1;
                            pairs.add(new Pair(i, j));
                    }
                }
            }
        }

        for (int i = 0; i < n; i++) {
            for (int j = 0; j < m; j++) {
                if (a[i][j] != b[i][j]) {
                    System.out.println("-1");
                    System.exit(0);
                }
            }
        }

        System.out.println(pairs.size());
        for (int i = 0; i < pairs.size(); i++)
            System.out.println(pairs.get(i).x + " " + pairs.get(i).y);

        input.close();
    }

    static class Pair {
        public int x, y;

        public Pair(int x, int y) {
            this.x = x;
            this.y = y;
        }
    }
}