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 Solution {
    public static void main(String args[]) {
      Scanner in = new Scanner(System.in);
      int n = in.nextInt();
      int m = in.nextInt();
      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] = in.nextInt();
          }
      }
      ArrayList<Integer> x = new ArrayList<Integer>();
      ArrayList<Integer> y = new ArrayList<Integer>();
      for(int i = 0; i < n; i++)
      {
          for(int j = 0; j < m; j++)
          {
              if(i + 1 < n && j + 1 < m)
              {
                  if(a[i][j] == 1 && a[i][j + 1] == 1 && a[i + 1][j] == 1 && a[i + 1][j + 1] == 1)
                  {
                     b[i][j] = 1; b[i][j + 1] = 1; b[i + 1][j] = 1; b[i + 1][j + 1] = 1;
                     x.add(i + 1); y.add(j + 1);
                  }
              }
          }
      }
      int opr = 0;
      for(int i = 0; i < n; i++)
      {
          boolean flag = false;
          for(int j = 0; j < m; j++)
          {
              if(a[i][j] != b[i][j])
              {
                  opr = -1;
                  flag = true;
                  break;
              }
          }
          if(flag) break;
      }
      if(opr == -1)
      {
          System.out.println(opr);
      }else{
          System.out.println(x.size());
          for(int i = 0; i < x.size(); i++)
          {
              System.out.println(x.get(i) + " " + y.get(i));
          }
      }
    }
}