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.awt.Point;
import java.math.BigInteger;
import java.util.ArrayList;
import java.util.Arrays;
import java.util.HashMap;
import java.util.Iterator;
import java.util.Scanner;
import javafx.util.Pair;



public class TwoNums {
    
   private static int[][] a;
   private static int[][] b;
   private static ArrayList  resX;
   private static ArrayList resY;
   

    
    public static void main(String[] args) {
         Scanner s = new Scanner(System.in);
         int n = s.nextInt();
         int m = s.nextInt();
          a = new int[n][m];
          b = new int[n][m];
          resX = new ArrayList <Integer>();
          resY = new ArrayList <Integer>();
         
         for (int i=0;i<n;i++){
             for(int j=0;j<m;j++){
                 
                 a[i][j] = s.nextInt();
                 b[i][j] = 0;
                 
             }
         }
             
         
          for (int i=0;i<n-1;i++){
        
                 for (int j=0;j<m-1;j++){
                     
                     if (a[i][j]+a[i+1][j]+a[i][j+1]+a[i+1][j+1]==4){
                        b[i][j] = 1;
                        b[i][j+1] = 1;
                        b[i+1][j] = 1;
                        b[i+1][j+1] = 1;
                        resX.add(i+1);
                        resY.add(j+1);
                     
                     }
                   
                 }
          }
               
             
             int diff = 0;
             
             
             for (int k=0;k<n;k++){
             for(int j=0;j<m;j++){
                 
                 if (a[k][j] != b[k][j]){
                 
                    diff++;
                 }
                 
                 
             }
             
         }
             
             if (diff == 0){
                 
                 System.out.println(resX.size());
                 
                 for (int k=0;k<resX.size();k++){
                 
                     System.out.println(resX.get(k)+" "+resY.get(k));
                 }
             
             }
             
             else{System.out.println(-1);}
             
         }

    
 
}
