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.ArrayList;
import java.util.StringTokenizer;

public class squareFilling {

    static class Point{
        int x;
        int y;
        Point(int x, int y){
            this.x = x;
            this.y = y;
        }
    }

    public static void main(String[] args) throws IOException {
        BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
        StringTokenizer st = new StringTokenizer(br.readLine());
        int n = Integer.parseInt(st.nextToken());
        int m = Integer.parseInt(st.nextToken());
        boolean[][] a = new boolean[n][m];
        for (int i = 0; i < n; i++) {
            st = new StringTokenizer(br.readLine());
            for (int j = 0; j < m; j++) {
                a[i][j] = Integer.parseInt(st.nextToken()) == 1;
            }
        }
        boolean[][] b = new boolean[n][m];
        int[] xchange = {0, 0, 1, 1};
        int[] ychange = {0, 1, 0, 1};
        ArrayList<Point> ans = new ArrayList<Point>();
        for (int i = 0; i < n; i++) {
            loop1: for (int j = 0; j < m; j++) {
                for (int k = 0; k < 4; k++) {
                    if(i + xchange[k] >= n || j + ychange[k] >= m || !a[i + xchange[k]][j + ychange[k]]){
                        continue loop1;
                    }
                }
                ans.add(new Point(i + 1, j + 1));
                for (int k = 0; k < 4; k++) {
                    if(i + xchange[k] < n && j + ychange[k] < m)
                        b[i + xchange[k]][j + ychange[k]] = true;
                }
            }
        }
        for (int i = 0; i < n; i++) {
            for (int j = 0; j < m; j++) {
                if(a[i][j] != b[i][j]){
                    System.out.println(-1);
                    System.exit(0);
                }
            }
        }

        System.out.println(ans.size());
        for (int i = 0; i < ans.size(); i++) {
            System.out.println(ans.get(i).x + " " + ans.get(i).y);
        }



    }
}
