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.InputStream;
import java.io.InputStreamReader;
import java.util.ArrayList;
import java.util.StringTokenizer;

public class b {
	public static void main(String[] args) throws Exception {
		FastScanner in = new FastScanner(System.in);
		
		int n = in.nextInt();
		int m = in.nextInt();
		int[][] a = new int[n][m];
		for (int i = 0; i < n; i++)
			for (int j = 0; j < m; j++)
				a[i][j] = in.nextInt();
		
		int[][] b = new int[n][m];
		
		int cnt = 0;
		ArrayList<Integer> x = new ArrayList<Integer>();
		ArrayList<Integer> y = new ArrayList<Integer>();
		
		int[] dx = {0, 0, 1, 1};
		int[] dy = {0, 1, 0, 1};
		
		for (int i = 0; i < n - 1; i++) {
			for (int j = 0; j < m - 1; j++) {
				boolean good = true;
				for (int k = 0; k < 4; k++) {
					int toX = i + dx[k];
					int toY = j + dy[k];
					if (a[toX][toY] != 1)
						good = false;
				}
				if (good) {
					for (int k = 0; k < 4; k++) {
						int toX = i + dx[k];
						int toY = j + dy[k];
						b[toX][toY] = 1;
					}
					cnt++;
					x.add(i + 1);
					y.add(j + 1);
				}
			}
		}
		
		if (isEqual(a, b)) {
			System.out.println(cnt);
			for (int i = 0; i < x.size(); i++) {
				System.out.println(x.get(i) + " " + y.get(i));
			}
		}
		else {
			System.out.println(-1);
		}
		
	}
	
	static boolean isEqual(int[][] a, int[][] b) {
		for (int i = 0; i < a.length; i++)
			for (int j = 0; j < a[0].length; j++)
				if (a[i][j] != b[i][j])
					return false;
		return true;
	}
	
	static class FastScanner {
	    BufferedReader br;
	    StringTokenizer st;
		
	    public FastScanner(InputStream i) {
	        br = new BufferedReader(new InputStreamReader(i));
	        st = new StringTokenizer("");
	    }
				
	    public String next() throws IOException {
	        if(st.hasMoreTokens())
	            return st.nextToken();
	        else
	            st = new StringTokenizer(br.readLine());
	        return next();
	    }

	    public int nextInt() throws IOException {
	        return Integer.parseInt(next());
	    }
	    //#
	    public long nextLong() throws IOException {
	        return Long.parseLong(next());
	    }
	    public double nextDouble() throws IOException {
	        return Double.parseDouble(next());
	    }
	    //$
	}
}
