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.OutputStream;
import java.io.IOException;
import java.io.InputStream;
import java.io.PrintWriter;
import java.util.InputMismatchException;
import java.io.IOException;
import java.util.ArrayList;
import java.io.InputStream;

/**
 * Built using CHelper plug-in
 * Actual solution is at the top
 *
 * @author Kirill Antonov
 */
public class Main {
    public static void main(String[] args) {
        InputStream inputStream = System.in;
        OutputStream outputStream = System.out;
        InputReader in = new InputReader(inputStream);
        PrintWriter out = new PrintWriter(outputStream);
        TaskB solver = new TaskB();
        solver.solve(1, in, out);
        out.close();
    }

    static class TaskB {
        private final ArrayList<Pair> squares = new ArrayList<>(4);

        public void solve(int testNumber, InputReader in, PrintWriter out) {
            squares.add(new Pair(-1, -1));
            squares.add(new Pair(-1, 0));
            squares.add(new Pair(0, -1));
            squares.add(new Pair(0, 0));
            int n = in.readInt(), m = in.readInt();
            int[][] aMatrix = in.readIntTable(n, m);
            ArrayList<Pair> operations = new ArrayList<>();
            for (int row = 0; row < n; row++) {
                for (int col = 0; col < m; col++) {
                    if (aMatrix[row][col] == 1) {
                        Pair newOperation = getOperation(aMatrix, row, col);
                        if (newOperation == null) {
                            out.println(-1);
                            return;
                        }
                        operations.add(newOperation);
                    }
                }
            }
            out.println(operations.size());
            for (Pair op : operations) {
                out.print(op.first + 1);
                out.print(' ');
                out.println(op.second + 1);
            }
        }

        private Pair getOperation(int[][] aMatrix, int row, int col) {
            for (Pair squareShift : squares) {
                int row1 = row + squareShift.first;
                int col1 = col + squareShift.second;
                if (checkSquare(aMatrix, row1, col1)) {
                    return new Pair(row1, col1);
                }
            }
            return null;
        }

        private boolean checkSquare(int[][] aMatrix, int row, int col) {
            if ((row < 0) || (col < 0) || (row >= aMatrix.length) || (col >= aMatrix[0].length)) {
                return false;
            }
            if ((row >= aMatrix.length - 1) || (col >= aMatrix[0].length - 1)) {
                return false;
            }
            for (int i = 0; i < 2; i++) {
                for (int j = 0; j < 2; j++) {
                    if (aMatrix[row + i][col + j] == 0) {
                        return false;
                    }
                }
            }
            return true;
        }

        private class Pair {
            int first;
            int second;

            public Pair(int first, int second) {
                this.first = first;
                this.second = second;
            }

        }

    }

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

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

        public int[] readIntArray(int size) {
            int[] array = new int[size];
            for (int i = 0; i < size; i++) {
                array[i] = readInt();
            }
            return array;
        }

        public int[][] readIntTable(int rowCount, int columnCount) {
            int[][] table = new int[rowCount][];
            for (int i = 0; i < rowCount; i++) {
                table[i] = this.readIntArray(columnCount);
            }
            return table;
        }

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

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

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

        }

    }
}

