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.lang.reflect.Array;
import java.util.Scanner;
public class square{

    public static int getSquare(int A[][],int B[][],int n,int m,int ops[][]){
        int k = 0;
        for(int i=0; i < n-1;i++){
            for(int j = 0 ; j < m-1;j++){
                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+1][j] = 1;
                    B[i][j+1] = 1;
                    B[i+1][j+1] = 1;
                    k++;
                    ops[i][j] = 1;
                }
            }
        }


            return k;
            
            
        
    }


    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        String dims[] = sc.nextLine().split(" ");
        int A[][] = new int[Integer.parseInt(dims[0])][Integer.parseInt(dims[1])];
        int B[][] = new int[Integer.parseInt(dims[0])][Integer.parseInt(dims[1])];
        for(int i = 0 ; i < Integer.parseInt(dims[0]); i++ ){
            String arr[] = sc.nextLine().split(" ");
            int array[] = new int[arr.length];
            for( int k = 0 ; k < arr.length; k++){
                array[k] = Integer.parseInt(arr[k]);
            }
            
            A[i] = array;
            for(int j = 0 ; j < Integer.parseInt(dims[1]); j++){
                B[i][j] = 0;
            }
        }
        int ops[][] = new int[Integer.parseInt(dims[0])][Integer.parseInt(dims[1])];
        int temp = getSquare(A, B,Integer.parseInt(dims[0]),Integer.parseInt(dims[1]), ops);
        int x = 1;
        for(int a = 0 ; a <Integer.parseInt(dims[0]);a++ ){
            for(int b = 0 ; b<Integer.parseInt(dims[1]);b++){
                
                if(A[a][b]!=B[a][b]){
                    x = -1;
                }
            }
        }
        if(x == -1){
            System.out.println(x);
        }
        else{
            System.out.println(temp);
              for( int a = 0 ;a <Integer.parseInt(dims[0]) ;a++){
                for ( int b = 0 ; b < Integer.parseInt(dims[1]);b++){
                    if(ops[a][b] == 1){
                        System.out.println((a+1) + " " + (b+1));
                    }
                } 
             }

        }
    }
}