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.io.*;
public class b{
	static Scanner sc=new Scanner(System.in);
	public static void main(String args[]){
		int k=1;
		//k=sc.nextInt();
		while(k--!=0){
			solve();
		}
	}

	static void solve(){
		int n=sc.nextInt();
		int m=sc.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]=sc.nextInt();
				B[i][j]=0;
			}

		}
		int cnt=0,f=0;
		int row[]=new int[2500];
		int column[]=new int[2500];
		for(int i=0;i<n-1;i+=1){
			for(int j=0;j<m-1;j+=1){
				if(A[i][j]==1 && A[i+1][j]==1 && A[i][j+1]==1 && A[i+1][j+1]==1){
					row[cnt]=i+1;
					column[cnt]=j+1;
					cnt++;
					B[i][j]=1;
					B[i+1][j]=1;
					B[i][j+1]=1;
					B[i+1][j+1]=1;
				}

			}
		}

		
		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(cnt);
		for(int i=0;i<cnt;i++)
			System.out.println(row[i]+" "+column[i]);
			
		

	}
	static int[] initarray(int n){
		int A[]=new int[n];
		for(int i=0;i<n;i++)
			A[i]=sc.nextInt();
		return A;
	}
}
//System.out.println();