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.*;
import java.util.*;

import static java.lang.Math.*;

public class Main {

    void problem() {
        int n = in.nextInt();
        int m = in.nextInt();
        int[][] a = new int[n][m];
        for (int i = 0; i < n; i++) {
            for (int j = 0; j < m; j++) {
                a[i][j] = in.nextInt();
            }
        }

        int[][] b = new int[n][m];
        List<Integer> res1 = new ArrayList<>();
        List<Integer> res2 = new ArrayList<>();

        for (int i = 0; i < n - 1; i++) {
            for (int j = 0; j < m - 1; j++) {
                if (    a[i][j] == 1 &&
                        a[i+1][j] == 1 &&
                        a[i][j+1] == 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;
                    res1.add(i);
                    res2.add(j);
                }
            }
        }

        boolean eq = true;
        for (int i = 0; i < n; i++) {
            for (int j = 0; j < m; j++) {
                eq &= a[i][j] == b[i][j];
            }
        }

        if (eq) {
            out.println(res1.size());
            for (int i = 0; i < res1.size(); i++) {
                out.println((res1.get(i) + 1) + " " + (res2.get(i) + 1));
            }
        } else {
            out.println("-1");
        }
    }

    void run() {
        in = new FastScanner();
        out = new PrintWriter(System.out);
        problem();
        out.close();
    }

    class FastScanner {
        BufferedReader br;
        StringTokenizer st;

        public FastScanner() {
            br = new BufferedReader(new InputStreamReader(System.in));
        }

//        public FastScanner(String s) {
//            try {
//                br = new BufferedReader(new FileReader(s));
//            } catch (FileNotFoundException e) {
//                e.printStackTrace();
//            }
//        }

        public String nextToken() {
            while (st == null || !st.hasMoreTokens()) {
                try {
                    st = new StringTokenizer(br.readLine());
                } catch (IOException e) {
                }
            }
            return st.nextToken();
        }

        public int nextInt() {
            return Integer.parseInt(nextToken());
        }

        public long nextLong() {
            return Long.parseLong(nextToken());
        }

        public double nextDouble() {
            return Double.parseDouble(nextToken());
        }
    }

    public static void main(String[] args) {
        new Main().run();
    }

    FastScanner in;
    PrintWriter out;

}