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 {

	public static void main(String[] args) throws Exception {
		BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
		StringTokenizer st = new StringTokenizer(br.readLine());
		int n = Integer.parseInt(st.nextToken());
		int m = Integer.parseInt(st.nextToken());
		boolean[][] map = new boolean[n][m];
		for(int i = 0; i < n; i++){
			st = new StringTokenizer(br.readLine());
			for(int j = 0; j < m; j++){
				map[i][j] = Integer.parseInt(st.nextToken()) == 1;
			}
		}
		ArrayList<Integer> xs = new ArrayList<>();
		ArrayList<Integer> ys = new ArrayList<>();
		for(int i = 0; i < n-1; i++){
			for(int j = 0; j < m-1; j++){
				if(map[i][j] && map[i+1][j+1] && map[i][j+1] && map[i+1][j]){
					xs.add(i);
					ys.add(j);
				}
			}
		}
		int k = xs.size();
		boolean[][] check = new boolean[n][m];
		for(int i = 0; i < k; i++){
			int x = xs.get(i);
			int y = ys.get(i);
			check[x][y] = true;
			check[x][y+1] = true;
			check[x+1][y] = true;
			check[x+1][y+1] = true;
		}
		boolean res = true;
		for(int i = 0; i < n; i++){
			for(int j = 0; j < m; j++){
				if(check[i][j] != map[i][j]) res = false;
			}
		}
		BufferedWriter bw = new BufferedWriter(new OutputStreamWriter(System.out));
		if(res){
			bw.write(k+"\n");
			for(int i = 0; i < k; i++){
				int x = xs.get(i)+1;
				int y = ys.get(i)+1;
				bw.write(x+" "+y+"\n");
			}
		}
		else{
			bw.write("-1");
		}
		bw.flush();
	}

}
