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.math.BigInteger;
import java.util.*;
public class TEST{
	public static void main(String args []){
		Scanner sc = new Scanner(System.in);
		
		int n=sc.nextInt();
		int m=sc.nextInt();
		
		int A[][]=new int [n+1][m+1];
		int B[][]=new int [n+1][m+1];
		
		for(int i=1;i<=n;i++) {
			for(int j=1;j<=m;j++) {
				A[i][j]=sc.nextInt();
				//System.out.print(A[i][j]+" ");
				
			}
			//System.out.println();		
		}	
		int count=0;
		ArrayList<Integer> x=new ArrayList<Integer>();
		ArrayList<Integer> y=new ArrayList<Integer>();
		
		for(int i=1;i<=n;i++) {
			for(int j=1;j<=m;j++) {
				int a=i;
				int an=i+1;
				int b=j;
				int bn=j+1;
				if(an<=n&&bn<=m) {
					if(A[a][b]==1&&A[a][bn]==1&&A[an][b]==1&&A[an][bn]==1) {
						B[a][b]=1;
						B[a][bn]=1;
						B[an][b]=1;
						B[an][bn]=1;
						count++;
						x.add(a);
						y.add(b);
					}
				}else {
					continue;
				}
			}
		}	
		boolean t=true;
		for(int i=1;i<=n;i++) {
			for(int j=1;j<=m;j++) {
				if(A[i][j]!=B[i][j]) {
					t=false;
					break;
				}	
			}		
		}
		if(!t) {
			System.out.println("-1");
		}else {
			System.out.println(count);
			for(int i=0;i<count;i++) {
				System.out.println(x.get(i)+" "+y.get(i));
			}
			
		}
		
	}
	
	
}