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.*;

public class CF10_2 {
    public static BufferedReader br= new BufferedReader(new InputStreamReader(System.in));

    public static BufferedWriter wr = new BufferedWriter(new OutputStreamWriter(System.out));

    public static void main(String args[]) throws IOException {
        String c[] = br.readLine().split(" ");
        int n = Integer.parseInt(c[0]);
        int m = Integer.parseInt(c[1]);

        int matrix[][] = new int[n][m];

        for (int i = 0; i < n; i++) {
            String data[] = br.readLine().split(" ");
            for (int j = 0; j < m; j++) {
                matrix[i][j] = Integer.parseInt(data[j]);
            }
        }

        String steps = mark(matrix);
        if(steps.equals("")){
            wr.write("-1");
        }else{
            wr.write(steps);
        }

        wr.flush();
    }

    private static String mark(int[][] matrix) {
        StringBuilder solution = new StringBuilder();
        int n = matrix.length;
        int m = matrix[0].length;
        int cont = 0;
        for (int i = 0; i < n; i++) {
            for (int j = 0; j < m; j++) {
                boolean pos[] = new boolean[4];
                pos[0] = check(i,j,n,m,matrix);
                pos[1] = check(i+1,j,n, m, matrix);
                pos[2] = check(i,j+1,n, m, matrix);
                pos[3] = check(i+1,j+1,n, m, matrix);

                if(pos[0] && pos[1] && pos[2] && pos[3]){
                    set(i,j,n,m,matrix);
                    set(i+1,j,n,m,matrix);
                    set(i,j+1,n,m,matrix);
                    set(i+1,j+1,n,m,matrix);
                    solution.append((i+1)+" "+(j+1));
                    solution.append("\n");
                    cont++;
                }
            }
        }

        if(!verify(matrix)){
            return "";
        }
        solution.insert(0,cont+"\n");
        return solution.toString();
    }

    private static void set(int i, int j, int n, int m, int[][] matrix) {
        if(i<n && j<m){
            matrix[i][j] = 2;
        }
    }

    private static boolean check(int i, int j, int n, int m, int[][] matrix) {
        if(i>=n || j>=m){
            return false;
        }else{
            if(matrix[i][j] == 0) {
                return false;
            }else{
                return true;
            }
        }
    }

    private static boolean verify(int[][] matrix) {
        boolean solution = true;
        for (int i = 0; i < matrix.length && solution; i++) {
            for (int j = 0; j < matrix[0].length && solution; j++) {
                if(matrix[i][j] != 0 &&  matrix[i][j] != 2){
                    solution = false;
                }
            }

        }

        return solution;
    }
}
