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.ArrayList;
import java.util.Arrays;
import java.util.List;
import java.util.Scanner;

/**
 * @author: zhaoqing
 * @date: 2018/9/9
 * @time: 下午9:37
 */
public class B1207 {
    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        int n = sc.nextInt();
        int m = sc.nextInt();
        int[][] table =new int[n][m];
        int notZeroNum = 0;
        int changeNum = 0;
        for(int i=0;i<n;i++){
            for (int j=0;j<m;j++){
                int tmp=sc.nextInt();
                if (tmp>0){
                    notZeroNum++;
                }
                table[i][j]=tmp;
            }
        }
        List<List<Integer>> result = new ArrayList<>();
        for(int i=0;i<n-1;i++){
            for(int j=0;j<m-1;j++){
                if(table[i][j]>0 && table[i][j+1]>0 && table[i+1][j]>0&&table[i+1][j+1]>0){
                    if(table[i][j]==1){
                        table[i][j]=2;
                        changeNum++;
                    }
                    if(table[i][j+1]==1){
                        table[i][j+1]=2;
                        changeNum++;
                    }
                    if(table[i+1][j]==1){
                        table[i+1][j]=2;
                        changeNum++;
                    }
                    if(table[i+1][j+1]==1){
                        table[i+1][j+1]=2;
                        changeNum++;
                    }
                    result.add(Arrays.asList(i+1,j+1));
                }
            }
        }
        if(notZeroNum==changeNum){
            System.out.println(result.size());
            for(int i=0;i<result.size();i++){
                System.out.println(result.get(i).get(0));

                System.out.println(result.get(i).get(1));
            }
        }else {
            System.out.println(-1);
        }


    }
}
