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} 
/*
 * To change this license header, choose License Headers in Project Properties.
 * To change this template file, choose Tools | Templates
 * and open the template in the editor.
 */
//package Contests;

import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStreamReader;
import java.util.ArrayList;

/**
 *
 * @author Akhilesh
 */
public class B1207 {
    public static void main(String[] args) throws IOException{
        BufferedReader scan = new BufferedReader(new InputStreamReader(System.in));
        
        String str[] = scan.readLine().split("\\s+");
        
        int n = Integer.parseInt(str[0]);
        int m = Integer.parseInt(str[1]);
        
        int[][] a = new int[n][m], b = new int[n][m];
        
        for(int i = 0; i < n; i++){
            str = scan.readLine().split("\\s+");
            for(int j = 0; j < m; j++){
                a[i][j] = Integer.parseInt(str[j]);
            }
        }
        int num = 0;
        boolean poss = true;
        ArrayList<pair> list = new ArrayList<>();
        outer : for(int i = 0; i < n-1; i++){
            for(int j = 0; j < m-1; j++){
                if(a[i][j] > 0){
                    if(a[i+1][j] > 0 && a[i+1][j+1] > 0 && a[i][j+1] > 0){
                        list.add(new pair(i+1, j+1));
                        b[i][j] = 1;
                        b[i+1][j] = 1;
                        b[i][j+1] = 1;
                        b[i+1][j+1] = 1;
                        a[i][j] += 1;
                        a[i+1][j] += 1;
                        a[i][j+1] += 1;
                        a[i+1][j+1] += 1;
                        num += 1;
                    }else{
                        if(a[i][j] == 1){
                            poss = false;
                            break outer;
                        }
                    }
                }
            }
        }
        
        for(int i = 0; i < n; i++){
            if(a[i][m-1] == 1){
                poss = false;
            }
        }
        
        for(int i = 0; i < m; i++){
            if(a[n-1][i] == 1){
                poss = false;
            }
        }
        
        if(poss){
            System.out.println(num);
            for(int i = 0; i < list.size() && i < 2500; i++){
                pair p = list.get(i);
                System.out.println(p.i + " " + p.j);
            }
        }else{
            System.out.println(-1);
        }
    }
}

class pair{
    int i, j;
    pair(int a, int b){
        i = a;
        j = b;
    }
}