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} 
/*
 * To change this license header, choose License Headers in Project Properties.
 * To change this template file, choose Tools | Templates
 * and open the template in the editor.
 */
//package solution;

/**
 *
 * @author USER
 */

import java.util.*;
import java.lang.*;
import java.io.*;
import java.math.*;
import java.text.*;
public class Solution{     
    
    
   
    public static void main(String [] args){
        InputReader sc=new InputReader(System.in);
        //Scanner sc=new Scanner(System.in);
       // BufferedReader br = new BufferedReader(new InputStreamReader(System.in)); 
               //    Scanner sc=new Scanner(System.in);
        //BufferedReader br=new BufferedReader(new InputStreamReader(System.in));
        
        int t=1;
        while(t-->0){
            int row=sc.ni();
            int col=sc.ni();
            int [][]a=new int[row+1][col+1];
            int [][]b=new int[row+1][col+1];
            
            int count=0;
            Vector<String>prin=new Vector<>();
            for(int i=1;i<=row;i++){
                for(int j=1;j<=col;j++){
                    a[i][j]=sc.ni();
                    
                }
            }
            for(int i=1;i<row;i++){
                for(int j=1;j<col;j++){
                    if(a[i][j]!=0&&a[i+1][j]!=0&&a[i][j+1]!=0&&a[i+1][j+1]!=0){
                        b[i][j]=-1;
                        b[i+1][j]=-1;
                        b[i][j+1]=-1;
                        b[i+1][j+1]=-1;
                        prin.add(i+" "+j);
                        count++;
                    }
                    
                }
                
            }
            boolean bo=true;
            in:for(int i=1;i<=row;i++){
                for(int j=1;j<=col;j++){
                    if(a[i][j]+b[i][j]!=0){
                        bo=false;
                        System.out.println("-1");
                        break in;
                    }
                    
                }
            }
            if(bo){
                System.out.println(count);
                while(!prin.isEmpty()){
                    
                    System.out.println(prin.get(0));
                    prin.remove(0);
                    
                }
            }
            
        }
            
            
            
            
                
        w.close();
    

    }
    static class InputReader { 
        private final InputStream stream;
        private final byte[] buf = new byte[8192];
        private int curChar, snumChars;
        public InputReader(InputStream st) {
            this.stream = st;
        } 
        public int read() {
            if (snumChars == -1)
                throw new InputMismatchException();
            if (curChar >= snumChars) {
                curChar = 0;
                try {
                    snumChars = stream.read(buf);
                } 
                catch (IOException e) {
                    throw new InputMismatchException();
                }
                if (snumChars <= 0)
                    return -1;
            }
            return buf[curChar++];
        }
        public int ni() {
            int c = read();
            while (isSpaceChar(c)) {
                c = read();
            }
            int sgn = 1;
            if (c == '-') {
                sgn = -1;
                c = read();
            }
            int res = 0;
            do {
                res *= 10;
                res += c - '0';
                c = read();
            } while (!isSpaceChar(c));
            return res * sgn;
        } 
        public long nl() {
            int c = read();
            while (isSpaceChar(c)) {
            c = read();
            }
            int sgn = 1;
            if (c == '-') {
                sgn = -1;
                c = read();
            }
            long res = 0;
            do {
                res *= 10;
                res += c - '0';
                c = read();
            } while (!isSpaceChar(c));
            return res * sgn;
        } 
        public int[] nia(int n) {
            int a[] = new int[n];
            for (int i = 0; i < n; i++) {
                a[i] = ni();
            }
            return a;
        } 
        public String rs() {
            int c = read();
            while (isSpaceChar(c)) {
                c = read();
            }
            StringBuilder res = new StringBuilder();
            do {
                res.appendCodePoint(c);
                    c = read();
            } while (!isSpaceChar(c));
            return res.toString();
        }
        public String nextLine() {
            int c = read();
            while (isSpaceChar(c))
                c = read();
            StringBuilder res = new StringBuilder();
            do {
                res.appendCodePoint(c);
                c = read();
            } while (!isEndOfLine(c));
            return res.toString();
        } 
        public boolean isSpaceChar(int c) {
            return c == ' ' || c == '\n' || c == '\r' || c == '\t' || c == -1;
        }
 
        private boolean isEndOfLine(int c) {
            return c == '\n' || c == '\r' || c == -1;
        } 
    }
    public static class Key {

        private final int x;
        private final int y;

        public Key(int x, int y) {
            this.x = x;
            this.y = y;
        }

        @Override
        public boolean equals(Object o) {
            if (this == o) return true;
            if (!(o instanceof Key)) return false;
            Key key = (Key) o;
            return x == key.x && y == key.y;
        }

        @Override
        public int hashCode() {
            int result = x;
            result = 31 * result + y;
            return result;
        }

    }
    
    static PrintWriter w = new PrintWriter(System.out);
    static long mod=998244353L,mod1=1000000007;
    static int co[][];
    static void dsort(){
        Arrays.parallelSort(co,(o1,o2)->o1[0]!=o2[0]?o1[0]-o2[0]:o1[1]-o2[1]);
    }
     static long  power(long x, long y) { 
        long temp=0; 
        if( y == 0) 
            return 1; 
        temp = power(x, y/2); 
        if (y%2 == 0) 
            return (temp*temp)%mod1; 
        else
            return (((x*temp)%mod1)*temp)%mod1; 
    } 
    static long modInverse(long a, long m){
        long num=m;
        long x=1;
        long power=a%mod1;
        while(num>0){
              if(num%2==1){
                  x=(x*power)%mod1;
            }
            num>>=1;
            power=(power*power)%mod1;         
        }
        return x;
    }
    static long ncrWithoutMod(int n,int r){
        if(n<r)return 0L;
        long ans=fact[n]/(fact[r]*fact[n-r]);
        return ans;
    }
    static long fact[]=new long[1000005];
    public static void findFact(){
        fact[0]=1;
        for(int i=1;i<=1000000;i++){
            fact[i]=(i*fact[i-1])%mod1;
        }
    }
    

                
 
class MySort {
    
    public void mergeSort(int []a,int left,int right){
        if(left<right){
            int m=(left+right)/2;
            mergeSort(a, left, m);
            mergeSort(a, m+1, right);
            merging(a,left,m,right);
            
        }
        
        
    }
    private void merging(int[]a,int left,int m,int right){
        int n1=m-left+1;
        int n2=right-(m+1)+1;
        int []L=new int[n1];
        int []R=new int[n2];
        
        for(int i=0;i<n1;i++){L[i]=a[left+i];}
        for(int i=0;i<n2;i++){R[i]=a[m+1+i];}
        
        int i=0;int j=0;
        int k=left;
        while(i<n1&&j<n2){
            if(L[i]<=R[j]){
                a[k]=L[i];
                i++;
            }
            else {
                a[k]=R[j];
                j++;
            }
            k++;
        }
        
        while(i<n1){
            a[k]=L[i];
            i++;
            k++;
        }
        while(j<n2){
            a[k]=R[j];
            j++;
            k++;
        }
    }
    
}
}
                
