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} 
////////////////////////////////////////////////////
//                                                //
//  For her who keeps the fire kindling in me...  //
//                                                //
////////////////////////////////////////////////////


import java.io.BufferedReader;
import java.io.BufferedWriter;
import java.io.FileOutputStream;
import java.io.IOException; 
import java.io.InputStreamReader;
import java.io.OutputStream;
import java.io.OutputStreamWriter;
import java.io.PrintWriter;
// import java.util.Scanner;
// import java.util.Arrays;
// import java.util.ArrayList;
// import java.util.Collections; 
// import java.util.StringTokenizer;
import java.util.*;
import java.lang.Math;
import java.awt.Point;
import java.awt.geom.*;

public class Main{

    public static void main(String args[]){
         try{
            FastReader s = new FastReader();
            BufferedWriter w = new BufferedWriter(new OutputStreamWriter(System.out));
            //long a, b, hcf;
            long ans;
            int  t, q, i, j,n, m, ai, aj, bi ,bj, ci, cj, di, dj, ei, ej, fi, fj, gi, gj,  hi, hj, ki, kj, size;
            //double x1, y1, r1, x2, y2, r2, dis, c, ax1, ay1, ax2, ay2, chk;
            boolean abs, fir, sec, thi, fou;
            
            n = s.nextInt();
            m = s.nextInt();
            int A[][] = new int[n][m];
            
            ArrayList<Integer> xans = new ArrayList<Integer>();
            ArrayList<Integer> yans = new ArrayList<Integer>();
            
            for(i=0; i<n; i++)
                for(j=0; j<m; j++)
                    A[i][j] = s.nextInt();
            
            abs = true;
            for(i=0; i<n; i++){
                for(j=0; j<m; j++){
                    ai = i-1; aj = j-1;
                    bi = i-1; bj = j;
                    ci = i-1; cj = j+1;
                    di = i; dj = j-1;
                    ei = i; ej = j;
                    fi = i; fj = j+1;
                    gi = i+1; gj = j-1;
                    hi = i+1; hj = j;
                    ki = i+1; kj = j+1;
                    if(A[i][j] == 1){
                        if(ai>=0&&ai<n && aj>=0&&aj<m && bi>=0&&bi<n && bj>=0&&bj<m && di>=0&&di<n && dj>=0&&dj<m && ei>=0&&ei<n && ej>=0&&ej<m
                            && A[ai][aj]==1 && A[bi][bj]==1 &&  A[di][dj]==1 &&  A[ei][ej]==1){
                                xans.add(ai);   yans.add(aj);
                                continue;
                            }
                        else if(ci>=0&&ci<n && cj>=0&&cj<m && bi>=0&&bi<n && bj>=0&&bj<m && fi>=0&&fi<n && fj>=0&&fj<m && ei>=0&&ei<n && ej>=0&&ej<m
                            && A[ci][cj]==1 && A[bi][bj]==1 &&  A[fi][fj]==1 &&  A[ei][ej]==1){
                                xans.add(bi);   yans.add(bj);
                                continue;
                        }else if(di>=0&&di<n && dj>=0&&dj<m && ei>=0&&ei<n && ej>=0&&ej<m && gi>=0&&gi<n && gj>=0&&gj<m && hi>=0&&hi<n && hj>=0&&hj<m
                            && A[di][dj]==1 && A[ei][ej]==1 &&  A[gi][gj]==1 &&  A[hi][hj]==1){
                                xans.add(di);   yans.add(dj);
                                continue;
                        }else if(ei>=0&&ei<n && ej>=0&&ej<m && fi>=0&&fi<n && fj>=0&&fj<m && hi>=0&&hi<n && hj>=0&&hj<m && ki>=0&&ki<n && kj>=0&&kj<m
                            && A[ei][ej]==1 && A[fi][fj]==1 &&  A[hi][hj]==1 &&  A[ki][kj]==1){
                                xans.add(ei);   yans.add(ej);
                                continue;
                        }
                        else{
                            abs = false;
                            break;
                        }
                    }
                }
                if(!abs)
                    break;
            }

            if(abs){
                size = xans.size();
                w.write(size+"\n");
                for(i=0; i<size; i++)
                    w.write((xans.get(i)+1)+" "+(yans.get(i)+1)+"\n");
            }else
                w.write("-1\n");
            
            //w.write(x+"\n");
            w.close();
        }catch(Exception e){
            e.printStackTrace();
        }
    }
}
                
                
//========================================### FAST IO ###=========================================//
class FastReader 
{ 
    BufferedReader br; 
    StringTokenizer st; 

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

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

    int nextInt() 
    { 
        return Integer.parseInt(next()); 
    } 

    long nextLong() 
    { 
        return Long.parseLong(next()); 
    } 

    Double nextDouble() 
    { 
        return Double.parseDouble(next());
    } 

    String nextLine() 
    { 
        String str = ""; 
        try
        { 
            str = br.readLine(); 
        } 
        catch (IOException e) 
        { 
            e.printStackTrace(); 
        } 
        return str;
    } 
}
    //====================================================================================================//