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} 
// Working program using Reader Class
import java.io.DataInputStream;
import java.io.FileInputStream;
import java.io.IOException;
import java.io.InputStreamReader;
import java.util.*;

public class Main2
{
    static class Reader
    {
        final private int BUFFER_SIZE = 1 << 16;
        private DataInputStream din;
        private byte[] buffer;
        private int bufferPointer, bytesRead;

        public Reader()
        {
            din = new DataInputStream(System.in);
            buffer = new byte[BUFFER_SIZE];
            bufferPointer = bytesRead = 0;
        }

        public Reader(String file_name) throws IOException
        {
            din = new DataInputStream(new FileInputStream(file_name));
            buffer = new byte[BUFFER_SIZE];
            bufferPointer = bytesRead = 0;
        }

        public String readLine() throws IOException
        {
            byte[] buf = new byte[64]; // line length
            int cnt = 0, c;
            while ((c = read()) != -1)
            {
                if (c == '\n')
                    break;
                buf[cnt++] = (byte) c;
            }
            return new String(buf, 0, cnt);
        }

        public int nextInt() throws IOException
        {
            int ret = 0;
            byte c = read();
            while (c <= ' ')
                c = read();
            boolean neg = (c == '-');
            if (neg)
                c = read();
            do
            {
                ret = ret * 10 + c - '0';
            } while ((c = read()) >= '0' && c <= '9');

            if (neg)
                return -ret;
            return ret;
        }

        public long nextLong() throws IOException
        {
            long ret = 0;
            byte c = read();
            while (c <= ' ')
                c = read();
            boolean neg = (c == '-');
            if (neg)
                c = read();
            do {
                ret = ret * 10 + c - '0';
            }
            while ((c = read()) >= '0' && c <= '9');
            if (neg)
                return -ret;
            return ret;
        }

        public double nextDouble() throws IOException
        {
            double ret = 0, div = 1;
            byte c = read();
            while (c <= ' ')
                c = read();
            boolean neg = (c == '-');
            if (neg)
                c = read();

            do {
                ret = ret * 10 + c - '0';
            }
            while ((c = read()) >= '0' && c <= '9');

            if (c == '.')
            {
                while ((c = read()) >= '0' && c <= '9')
                {
                    ret += (c - '0') / (div *= 10);
                }
            }

            if (neg)
                return -ret;
            return ret;
        }

        private void fillBuffer() throws IOException
        {
            bytesRead = din.read(buffer, bufferPointer = 0, BUFFER_SIZE);
            if (bytesRead == -1)
                buffer[0] = -1;
        }

        private byte read() throws IOException
        {
            if (bufferPointer == bytesRead)
                fillBuffer();
            return buffer[bufferPointer++];
        }

        public void close() throws IOException
        {
            if (din == null)
                return;
            din.close();
        }
    }


    private static long gcd(long a, long b){
        if(b==0){
            return a;
        }
        return gcd(b, a%b);
    }
    public static void main(String[] args) throws IOException
    {
        Reader z = new Reader();
        int n=z.nextInt(), m=z.nextInt(), i, j, flag=0, k=0;
        int[][] a = new int[n][m];
        int[][] b = new int[n][m];
        int[] x = new int[2600];
        int[] y = new int[2600];
        for(i=0;i<n;i++){
            for(j=0;j<m;j++){
                a[i][j]=z.nextInt();
            }
        }
        for(i=0;i<n;i++){
            for(j=0;j<m;j++){
                if(a[i][j]==1 && b[i][j]==0){
                    if(i>0 && j>0 && a[i-1][j-1]==1 && a[i-1][j]==1 && a[i][j-1]==1){
                        x[k]=i;
                        y[k]=j;
                        k++;
                        b[i][j]=1;
                        b[i-1][j-1]=1;
                        b[i-1][j]=1;
                        b[i][j-1]=1;
                    }
                    else if(i>0 && j+1<m && a[i-1][j]==1 && a[i-1][j+1]==1 && a[i][j+1]==1){
                        x[k]=i;
                        y[k]=j+1;
                        k++;
                        b[i][j]=1;
                        b[i-1][j]=1;
                        b[i-1][j+1]=1;
                        b[i][j+1]=1;
                    }
                    else if(i+1<n && j>0 && a[i][j-1]==1 && a[i+1][j-1]==1 && a[i+1][j]==1){
                        x[k]=i+1;
                        y[k]=j;
                        k++;
                        b[i][j]=1;
                        b[i][j-1]=1;
                        b[i+1][j-1]=1;
                        b[i+1][j]=1;
                    }
                    else if(i+1<n && j+1<m && a[i+1][j]==1 && a[i][j+1]==1 && a[i+1][j+1]==1){
                        x[k]=i+1;
                        y[k]=j+1;
                        k++;
                        b[i][j]=1;
                        b[i+1][j]=1;
                        b[i+1][j+1]=1;
                        b[i][j+1]=1;
                    }
                    else {
                        flag=1;
                        break;
                    }
                }
            }
        }
        if(flag==1){
            System.out.println(-1);
        }
        else {
            System.out.println(k);
            for(i=0;i<k;i++){
                System.out.println(x[i]+" "+y[i]);
            }
        }
    }
}