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.io.BufferedReader;
import java.io.IOException;
import java.io.InputStreamReader;
import java.util.Scanner;
import java.util.StringTokenizer;

/**
 *
 * @author Ebrahim
 */
public class BSquareFilling {

    /**
     * @param args the command line arguments
     */
    public static int grid[][] = new int[60][60];
    public static int n, m, k = 0;    
    public static int ans[][] = new int[60][60];
    public static Scanner inp = new Scanner(System.in);
    public static void main(String[] args) throws IOException {
        // TODO code application logic here
        
        n = inp.nextInt();
        m = inp.nextInt();
        for(int i = 1; i <= n; i++){
            for(int j = 1; j <= m; j++){
                grid[i][j] = inp.nextInt();
            }
        }
        for(int i = 1; i <= n; i++){
            for(int j = 1; j <= m; j++){
                if(grid[i][j] == 0)
                    continue;
                if(rightUp(i, j)){
                    if(ans[i - 1][j - 1] == 0){
                        k++;
                        ans[i - 1][j - 1] = 1;
                    }
                }else if(leftUp(i, j)){
                    if(ans[i - 1][j] == 0){
                        k++;
                        ans[i - 1][j] = 1;
                    }
                }else if(rightDown(i, j)){
                    if(ans[i][j - 1] == 0){
                        k++;
                        ans[i][j - 1] = 1;
                    }
                }else if(leftDown(i, j)){
                    if(ans[i][j] == 0){
                        k++;
                        ans[i][j] = 1;
                    }
                }else{
                    System.out.println("-1");
                    return;
                }
            }
        }
        System.out.println(k);
        for(int i = 1; i <= n; i++){
            for(int j = 1; j <= m; j++){
                if(ans[i][j] == 1){
                    System.out.printf("%d %d\n",i,j);
                }
            }
        }
        
    }
    
    public static boolean rightUp(int x, int y){
        if(x == 1 || y == 1)
            return false;
        if(x > 0 && y > 0 && grid[x - 1][y - 1] == 0)
            return false;
        if(x > 0 && grid[x - 1][y] == 0)
            return false;
        if(y > 0 && grid[x][y - 1] == 0)
            return false;
        return true;
    }
    
    public static boolean leftUp(int x, int y){
        if(x == 1 || y == m)
            return false;
        if(x > 0 && y < m && grid[x - 1][y + 1] == 0)
            return false;
        if(x > 0 && grid[x - 1][y] == 0)
            return false;
        if(y < m && grid[x][y + 1] == 0)
            return false;
        return true;
    }
    
    public static boolean rightDown(int x, int y){
        if(x == n || y == 1)
            return false;
        if(x < n && y > 0 && grid[x + 1][y - 1] == 0)
            return false;
        if(x < n && grid[x + 1][y] == 0)
            return false;
        if(y > 0 && grid[x][y - 1] == 0)
            return false;
        return true;
    }
    
    public static boolean leftDown(int x, int y){
        if(x == n || y == m)
            return false;
        if(x < n && y < m && grid[x + 1][y + 1] == 0)
            return false;
        if(x < n && grid[x + 1][y] == 0)
            return false;
        if(y < m && grid[x][y + 1] == 0)
            return false;
        return true;
    }
 
}
