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.*;
import java.lang.*;
// StringBuilder uses java.lang
 
 
public class mainClass {
    
    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        StringBuilder st=new StringBuilder();
        int m = sc.nextInt();
        int n = sc.nextInt();
        ArrayList<ArrayList<Integer>> ok = new ArrayList<>();
        ArrayList<ArrayList<Integer>> ok2 = new ArrayList<>();
        ArrayList<Integer> empty = new ArrayList<>();
        ArrayList<Integer> empty2 = new ArrayList<>();
        ArrayList<Integer> empty3 = new ArrayList<>();
        ArrayList<Integer> empty4 = new ArrayList<>();   
        ok.add(empty);
        ok2.add(empty2);
        for(int i=0;i<m;i++) {
            ArrayList<Integer> row = new ArrayList<>();
            ArrayList<Integer> row2 = new ArrayList<>();            
            for (int j=0;j<n;j++) {
                int t=sc.nextInt();
                if (t==1) {
                    row.add(j);
                    row2.add(j);
                }
            }
            ok.add(row);
            ok2.add(row2);
        }
        ok.add(empty3);
        ok2.add(empty4);
        boolean pos = true;
        ArrayList<ArrayList<Integer>> listSol = new ArrayList<>();
        for (int i=1;i<m+1;i++) {
            while (ok.get(i).size()>0) {
                ArrayList<Integer> u = new ArrayList<>();
                int z=ok.get(i).get(0);
                if (ok2.get(i).contains(ok.get(i).get(0)-1) && ok2.get(i+1).contains(ok.get(i).get(0)-1) && ok2.get(i+1).contains(ok.get(i).get(0))) {
                    u.add(i);
                    u.add(ok.get(i).get(0));
                    listSol.add(u);
                } else if (ok2.get(i).contains(ok.get(i).get(0)+1) && ok2.get(i+1).contains(ok.get(i).get(0)+1) && ok2.get(i+1).contains(ok.get(i).get(0))) {
                    u.add(i);
                    u.add(ok.get(i).get(0)+1);
                    listSol.add(u);
                } else if (ok2.get(i).contains(ok.get(i).get(0)-1) && ok2.get(i-1).contains(ok.get(i).get(0)-1) && ok2.get(i-1).contains(ok.get(i).get(0))) {
                    u.add(i-1);
                    u.add(ok.get(i).get(0));
                    listSol.add(u);
                } else if (ok2.get(i).contains(ok.get(i).get(0)+1) && ok2.get(i-1).contains(ok.get(i).get(0)+1) && ok2.get(i-1).contains(ok.get(i).get(0))) {
                    u.add(i-1);
                    u.add(ok.get(i).get(0)+1);
                    listSol.add(u);
                } else {
                    pos = false;
                    break;
                }
                ok.get(i).remove(0);
            }
        }
        if (pos==false) {
            System.out.println("-1");
        } else {
            System.out.println(listSol.size());
            for (int i=0;i<listSol.size();i++) {
                System.out.print(listSol.get(i).get(0));
                System.out.print(" ");
                System.out.println(listSol.get(i).get(1));
            }
        }
    }
}