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.lang.*;
import java.io.*;
import java.math.*;

public class Q2 {

	static PrintWriter pw = new PrintWriter(new OutputStreamWriter(System.out));

	static class FastScanner {
		private InputStream stream;
		private byte[] buf = new byte[1024];
		private int curChar;
		private int numChars;
		private SpaceCharFilter filter;

		public FastScanner(InputStream stream) {
			this.stream = stream;
		}

		public static boolean isWhitespace(int c) {
			return c == ' ' || c == '\n' || c == '\r' || c == '\t' || c == -1;
		}

		public int read() {
			if (numChars == -1)
				throw new InputMismatchException();
			if (curChar >= numChars) {
				curChar = 0;
				try {
					numChars = stream.read(buf);
				} catch (IOException e) {
					throw new InputMismatchException();
				}
				if (numChars <= 0)
					return -1;
			}
			return buf[curChar++];
		}

		public int nextInt() {
			int c = read();
			while (isSpaceChar(c))
				c = read();
			int sgn = 1;
			if (c == '-') {
				sgn = -1;
				c = read();
			}
			int res = 0;
			do {
				if (c < '0' || c > '9')
					throw new InputMismatchException();
				res *= 10;
				res += c - '0';
				c = read();
			} while (!isSpaceChar(c));
			return res * sgn;
		}

		public long nextLong() {
			int c = read();
			while (isSpaceChar(c))
				c = read();
			int sgn = 1;
			if (c == '-') {
				sgn = -1;
				c = read();
			}
			long res = 0;
			do {
				if (c < '0' || c > '9')
					throw new InputMismatchException();
				res *= 10;
				res += c - '0';
				c = read();
			} while (!isSpaceChar(c));
			return res * sgn;
		}

		public String nextToken() {
			int c = read();
			while (isSpaceChar(c))
				c = read();
			StringBuilder res = new StringBuilder();
			do {
				res.appendCodePoint(c);
				c = read();
			} while (!isSpaceChar(c));
			return res.toString();
		}

		public boolean isSpaceChar(int c) {
			if (filter != null)
				return filter.isSpaceChar(c);
			return isWhitespace(c);
		}

		public interface SpaceCharFilter {
			public boolean isSpaceChar(int ch);
		}
	}

	static class Pair implements Comparable<Pair> {
		int u, v;

		public Pair(int u, int v) {
			this.u = u;
			this.v = v;
		}

		public int compareTo(Pair o) {
			return Integer.compare(u, o.u) != 0 ? Integer.compare(u, o.u) : Integer.compare(v, o.v);
		}
	}

	public static void main(String[] args) throws Exception {
		FastScanner fs = new FastScanner(System.in);

		int n = fs.nextInt(), m = fs.nextInt();
		int[][] arr = new int[n][m], brr = new int[n][m];
		for (int i = 0; i < n; i++)
			for (int j = 0; j < m; j++)
				arr[i][j] = fs.nextInt();

		ArrayList<Integer> idxI = new ArrayList<Integer>(), idxJ = new ArrayList<Integer>();
		for (int i = 0; i < n - 1; i++) {
			for (int j = 0; j < m - 1; j++) {
				if (arr[i][j] == 1 && arr[i + 1][j] == 1 && arr[i][j + 1] == 1 && arr[i + 1][j + 1] == 1) {
					brr[i][j] = 1;
					brr[i + 1][j] = 1;
					brr[i][j + 1] = 1;
					brr[i + 1][j + 1] = 1;

					idxI.add(i);
					idxJ.add(j);
				}
			}
		}

		boolean flag = true;
		for (int i = 0; i < n; i++) {
			for (int j = 0; j < m; j++) {
				if (arr[i][j] != brr[i][j]) {
					flag = false;
					break;
				}
			}
		}

		if (!flag)
			pw.println(-1);
		else {
			int sz = idxI.size();
			pw.println(sz);
			for (int i = 0; i < sz; i++)
				pw.println((idxI.get(i) + 1) + " " + (idxJ.get(i) + 1));
		}

		pw.flush();
		pw.close();
	}

}