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.io.PrintWriter;
import java.util.Iterator;
import java.util.StringTokenizer;

public class qq {
	static int n;
	static int m;
	static int b[][];
	static int a[][];		
	public static boolean valid(int x,int y) {
		return (x<n&&x>-1&&y<m&&y>-1);
	}
	
	public static boolean tt(int x,int y) {
		if(valid(x,y))
		if(a[x][y]==1) {
			if(valid(x,y)&&valid(x,y+1)&&valid(x+1,y)&&valid(x+1,y+1)) {
				if(a[x][y+1]==1&&a[x+1][y]==1&&a[x+1][y+1]==1) {
					return true;
				}			
			}
		}
		return false;
	}
	
	public static void main(String[] args) throws IOException {
		BufferedReader br=new BufferedReader(new InputStreamReader(System.in));
		PrintWriter pw=new PrintWriter(System.out);
		StringTokenizer st=new StringTokenizer(br.readLine());
		n=Integer.parseInt(st.nextToken());
		m=Integer.parseInt(st.nextToken());
		a=new int [n][m];
		b=new int [n][m];
		for (int i = 0; i < n; i++) {
			st=new StringTokenizer(br.readLine());
			for (int j = 0; j < m; j++) {
				a[i][j]=Integer.parseInt(st.nextToken()); 
			}
		}
		int k=0;
		int q[][]=new int[55][55];
		for (int i = 0; i < n; i++) {
			//Bx,y, Bx,y+1, Bx+1,y and  Bx+1,y+1
			for (int j = 0; j < m; j++) {
				int x=i;int y=j;
				if(a[x][j]==1) {
					if(tt(x,y)) {
						k++;
						q[x][y]=1;
					}
					else {
						x=i-1;y=j-1;
						if(tt(x,y)) {
							k++;
							q[x][y]=1;
						}
						else {
							x=i;y=j-1;
							if(tt(x,y)) {
								k++;
								q[x][y]=1;
							}
							else {
								x=i-1;y=j;
								if(tt(x,y)) {
									k++;
									q[x][y]=1;
								}
								else {
									x=i-1;y=j-1;
									if(tt(x,y)) {
										k++;
										q[x][y]=1;
									}
									else {
										pw.println(-1);
										pw.flush();
										return;
									}
								}
							}
						}
							
					}
				}	
			}
		}
		k=0;
		for (int i = 0; i < q.length; i++) {
			
			for (int j = 0; j < q.length; j++) {
				if(q[i][j]==1)
					k++;
				}
		}
		pw.println(k);
for (int i = 0; i < q.length; i++) {
			
			for (int j = 0; j < q.length; j++) {
				if(q[i][j]==1)
					pw.println((i+1)+" "+(j+1));
			}
		}
		pw.flush();
	}
	
}
