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 {

    static class InputReader {
        BufferedReader reader;
        StringTokenizer tokenizer;

        public InputReader(InputStream stream) {
            reader = new BufferedReader(new InputStreamReader(stream), 32768);
            tokenizer = null;
        }

        String next() {
            while (tokenizer == null || !tokenizer.hasMoreTokens()) {
                try {
                    tokenizer = new StringTokenizer(reader.readLine());
                } catch (IOException e) {
                    throw new RuntimeException(e);
                }
            }
            return tokenizer.nextToken();
        }

        public int nextInt() {
            return Integer.parseInt(next());
        }

        public long nextLong() {
            return Long.parseLong(next());
        }

        public double nextDouble() {
            return Double.parseDouble(next());
        }
    }

    static InputReader r = new InputReader(System.in);
    static PrintWriter pw = new PrintWriter(System.out);

    public static void main(String[] args) {
        int n = r.nextInt();
        int m = r.nextInt();
        ArrayList<int[]> operations = new ArrayList<int[]>();
        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] = r.nextInt();
            }
        }
        for(int i = 0; i < n-1; i++){
            for(int j = 0; j < m-1; j++){
                if(a[i][j] == 1 && a[i+1][j] == 1 && a[i][j+1] == 1 && a[i+1][j+1] == 1){
                    b[i][j] = b[i+1][j] = b[i][j+1] = b[i+1][j+1] = 1;
                    operations.add(new int[]{i+1, j+1});
                }
            }
        }
        boolean fail = false;
        for(int i = 0; i < n; i++){
            for(int j = 0; j < m; j++){
                if(a[i][j] != b[i][j]){
                    fail = true;
                }
            }
        }
        if(fail){
            pw.println(-1);
        } else{
            pw.println(operations.size());
            for(int[] op : operations){
                pw.println(op[0] + " " + op[1]);
            }
        }
        pw.close();
    }
}

/**
*                _        _                 _                                                
*               | |      | |               | |                                               
*   ___ ___   __| | ___  | |__  _   _    __| | __ _ _ __ _ __ ___ _ __     _   _  __ _  ___  
*  / __/ _ \ / _` |/ _ \ | '_ \| | | |  / _` |/ _` | '__| '__/ _ \ '_ \   | | | |/ _` |/ _ \ 
* | (_| (_) | (_| |  __/ | |_) | |_| | | (_| | (_| | |  | | |  __/ | | |  | |_| | (_| | (_) |
*  \___\___/ \__,_|\___| |_.__/ \__, |  \__,_|\__,_|_|  |_|  \___|_| |_|   \__, |\__,_|\___/ 
*                                __/ |                               ______ __/ |            
*                               |___/                               |______|___/             
 */