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.io.PrintWriter;


import java.util.*;



public class Main {

    static boolean[][]vis;
    static int x,y,m;
    static int ans=Integer.MAX_VALUE;
    static char[][]a;
    static int dx[]={1,-1,0,0};
    static int []dy={0,0,1,-1};
    static void dfs(int r,int c,int sum){
        if (r<0||r>=m||c<0||c>=m||vis[r][c])return;
        if (a[r][c]=='3'){
            ans=Math.min(ans,sum);
            return;
        }
        vis[r][c]=true;
        for (int i = 0; i < 4; i++) {
            dfs(dx[i]+r,dy[i]+c,sum+1);
        }
    }



        public static void main (String[]args) throws IOException {
            Scanner in = new Scanner(System.in);


            try (PrintWriter or = new PrintWriter(System.out)) {
                int n=in.nextInt(),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();
                    }
                }
                ArrayList<Pair>ans= new ArrayList<>();
                boolean[][]state=new boolean[n][m];
                for (int i = 0; i < n; i++) {
                    for (int j = 0; j < m; j++) {
                        if (a[i][j]==0){
                            if (i-1>=0) state[i-1][j]=true;
                            if (i-1>=0&&j-1>=0)state[i-1][j-1]=true;
                        }
                    }
                }
                int [][]b= new int[n][m];
                for (int i = 0; i < n; i++) {
                    for (int k = 0; k < m; k++) {
                        if (a[i][k]==1&&(i+1<n&&k+1<m)&&!state[i][k]
                        &&a[i+1][k]==a[i][k]
                                && a[i+1][k+1]==a[i][k]
                                &&a[i][k+1]==a[i][k]
                                ){
                            ans.add(new Pair(i+1,k+1));
                            b[i][k]=b[i+1][k]=b[i][k+1]=b[i+1][k+1]=1;
                        }
                    }
                }
                for (int i = 0; i <n ; i++) {
                    for (int k = 0; k < m; k++) {
                        if (a[i][k]!=b[i][k]){
                            or.println(-1);
                            return;
                        }
                    }
                }
                or.println(ans.size());
                for(Pair p:ans)or.println(p.first+" "+p.second);








            }
        }


    static long gcd(long a, long b)
    {
        if (b == 0)
            return a;
        return gcd(b, a % b);
    }
    static int getlen(int r,int l,int a){
        return (r-l+1+1)/(a+1);
    }






    static class Scanner {

        StringTokenizer st;
        BufferedReader br;

        public Scanner(InputStream s) {
            br = new BufferedReader(new InputStreamReader(s));
        }

        public String next() throws IOException {
            while (st == null || !st.hasMoreTokens()) {
                st = new StringTokenizer(br.readLine());
            }
            return st.nextToken();
        }

        public int nextInt() throws IOException {
            return Integer.parseInt(next());
        }

        public long nextLong() throws IOException {
            return Long.parseLong(next());
        }

        public String nextLine() throws IOException {
            return br.readLine();
        }

        public double nextDouble() throws IOException {
            String x = next();
            StringBuilder sb = new StringBuilder("0");
            double res = 0, f = 1;
            boolean dec = false, neg = false;
            int start = 0;
            if (x.charAt(0) == '-') {
                neg = true;
                start++;
            }
            for (int i = start; i < x.length(); i++) {
                if (x.charAt(i) == '.') {
                    res = Long.parseLong(sb.toString());
                    sb = new StringBuilder("0");
                    dec = true;
                } else {
                    sb.append(x.charAt(i));
                    if (dec) {
                        f *= 10;
                    }
                }
            }
            res += Long.parseLong(sb.toString()) / f;
            return res * (neg ? -1 : 1);
        }

        public boolean ready() throws IOException {
            return br.ready();
        }

    }
}

class Pair  {
    int first, second,third;

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

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

class Tempo {

    String first;
    int second;

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