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 javafx.util.Pair;

import java.io.*;
import java.util.Deque;
import java.util.LinkedList;
import java.util.StringTokenizer;

public class Div2B71 {

    public static void main(String[] args) throws IOException {
        IoHandler ioHandler = new IoHandler();
        new Task().solve(ioHandler, ioHandler.out);
        ioHandler.out.close();
    }

    private static class Task {
        private void solve(IoHandler reader, PrintWriter writer) throws IOException {
            int n = reader.nextInt(), m = reader.nextInt();
            int[][] mat = new int[n][m];

            //read matrix
            for (int i = 0; i < n; i++) {
                for (int j = 0; j < m; j++) {
                    mat[i][j] = reader.nextInt();
                }
            }
            Deque<Pair<Integer, Integer>> deque = new LinkedList<>();
            //now iterate and check if 2*2 matrix ending at i,j is filled with 1, if so then include this in solution
            for (int i = 1; i < n; i++) {
                for (int j = 1; j < m; j++) {
                    if (mat[i - 1][j - 1] * mat[i - 1][j] * mat[i][j - 1] * mat[i][j] > 0) {
                        mat[i - 1][j - 1] = 2;
                        mat[i - 1][j] = 2;
                        mat[i][j - 1] = 2;
                        mat[i][j] = 2;

                        deque.addLast(new Pair<>(i, j));
                    }
                }
            }

            int count = 0;
            for (int i = 0; i < n; i++) {
                for (int j = 0; j < m; j++) {
                    if (mat[i][j] == 1) {
                        count++;
                    }
                }
            }

            if (count > 0) {
                writer.println(-1);
            } else {
                writer.println(deque.size());
                while (!deque.isEmpty()) {
                    Pair<Integer, Integer> index = deque.pollFirst();
                    writer.println(index.getKey() + " " + index.getValue());
                }
            }
        }
    }

    private static class IoHandler {
        private final PrintWriter out;
        private final BufferedReader reader;
        private StringTokenizer tokenizer;

        IoHandler() throws IOException {
            boolean local = new File("input").exists();
            InputStream stream = local ? new FileInputStream("input") : System.in;
            out = local ? new PrintWriter(new FileOutputStream("output")) : new PrintWriter(System.out);
            reader = new BufferedReader(new InputStreamReader(stream), 32768);
        }

        private String nextString() throws IOException {
            while (tokenizer == null || !tokenizer.hasMoreTokens()) {
                tokenizer = new StringTokenizer(reader.readLine());
            }
            return tokenizer.nextToken();
        }

        private int nextInt() throws IOException {
            return Integer.parseInt(nextString());
        }
    }
}
