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.Arrays;
import java.util.StringTokenizer;

public class Square_filling {
    static int a[][];
    static int b[][];
    public static void main(String afgs[]) throws IOException{
        process();
    }
    public static void process() throws IOException{
        BufferedReader in=new BufferedReader(new InputStreamReader(System.in));
        String input=in.readLine();
        StringTokenizer st=new StringTokenizer(input," ");
        int m=Integer.parseInt(st.nextToken());
        int n=Integer.parseInt(st.nextToken());
        a=new int[m][n];
        b=new int[m][n];
        for(int i=0;i<m;i++){
            input=in.readLine();
            st=new StringTokenizer(input," ");
            for(int j=0;j<n;j++)
                a[i][j]=Integer.parseInt(st.nextToken());
        }
        int c=0;
        int ans[][]=new int[999999][2];
        for(int i=0;i<m-1;i++){
            for(int j=0;j<n-1;j++){
                if(a[i][j]==1 && a[i][j+1]==1 && a[i+1][j]==1 && a[i+1][j+1]==1) {
                    ans[c][0]=i+1;
                    ans[c][1]=j+1;
                    c++;
                    b[i][j] = 1;
                    b[i][j + 1] = 1;
                    b[i + 1][j] = 1;
                    b[i + 1][j + 1] = 1;
                }
            }
        }
        if(!Arrays.deepEquals(a,b))
            System.out.println("-1");
        else if(Arrays.deepEquals(a,b) && c==0)
            System.out.println("0");
        else{
            System.out.println(c);
            int l=0;
            while(true){
                if(ans[l][0]==0)
                    break;
                else {
                    System.out.println(ans[l][0] + " " + ans[l][1]);
                    l++;
                }
            }
        }
    }
}
