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.ArrayList;
import java.util.Arrays;
import java.util.StringTokenizer;

public class Codechef{
    
    static 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()); 
		} 
	}
    
    static class Pair{
    		int x= 0;
    		int y = 0;
    		public Pair(int x, int y){
    			this.x = x;
    			this.y = y;
    		}
    }
    
    private static ArrayList<Pair> solve(int[][] A, int[][] B){
    		ArrayList<Pair> list = new ArrayList<>();
    		for(int i=0; i<A.length-1; i++){
    			for(int j=0; j<A[0].length-1; j++){
    				if(A[i][j]==1 && A[i][j+1]==1 && A[i+1][j]==1 && A[i+1][j+1]==1){
    					Pair pair = new Pair(i+1, j+1);
    					list.add(pair);
    					B[i][j] = 1;
    					B[i][j+1] = 1;
    					B[i+1][j] = 1;
    					B[i+1][j+1] = 1;
    				}
    			}
    		}
    		return list;
    }
    
    public static void main(String[] args){
        FastReader fastReader =new FastReader();
        int n = fastReader.nextInt();
        int m = fastReader.nextInt();
        int[][] A = new int[n][m];
        int[][] B = new int[n][m];
        for(int i=0; i<n; i++){
        		for(int j=0; j<m; j++){
        			A[i][j] = fastReader.nextInt();
        		}
        }
        ArrayList<Pair> list = solve(A, B);
        for(int i=0; i<n; i++){
        		for(int j=0; j<m; j++){
        			if(A[i][j] != B[i][j]){
        				System.out.println(-1);
        				return;
        			}
        		}
        }
        System.out.println(list.size());
        for(Pair p : list){
        		System.out.println(p.x+" "+p.y);
        }
        
    }
}