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.io.BufferedReader;
import java.io.IOException;
import java.io.InputStreamReader;

public class ar {

    static class FastReader {
        BufferedReader br;
        StringTokenizer st;

        public FastReader() {
            br = new BufferedReader(new InputStreamReader(System.in));
        }

        String next() {
            while (st == null || !st.hasMoreElements()) {
                try {
                    st = new StringTokenizer(br.readLine());
                } catch (final IOException e) {
                    e.printStackTrace();
                }
            }
            return st.nextToken();
        }

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

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

        double nextDouble() {
            return Double.parseDouble(next());
        }

        String nextLine() {
            String str = "";
            try {
                str = br.readLine();
            } catch (final IOException e) {
                e.printStackTrace();
            }
            return str;
        }
    }

    static boolean[] seen;
    static Map<Integer, Integer> map;
    static Map<Long, Long> lmap;
    static Set<Character> charset;
    static Set<Integer> set;
    static int[] arr;
    static int[][] dp;
    static int rem = (int) 1e9 + 7;
    static List<List<Integer>> graph;
    static int[][] kmv = { { 2, 1 }, { 1, 2 }, { 2, -1 }, { -1, 2 }, { -2, 1 }, { 1, -2 }, { -1, -2 }, { -2, -1 } };
    static char[] car;
    static boolean[] primes;
    static int MAX = (int) 1e4 + 1;
    static double[] dar;
    static long[] lar;
    static long[][] dlar;

    static void Sieve() {
        primes = new boolean[MAX];
        primes[0] = true;
        primes[1] = true;
        for (int i = 2; i * i < MAX; i++) {
            if (!primes[i]) {
                for (int j = i * i; j < MAX; j += i) {
                    primes[j] = true;
                }
            }
        }
    }

    public static void main(String[] args) throws java.lang.Exception {
        FastReader scn = new FastReader();
        int n = scn.nextInt();
        int m=scn.nextInt();
dp=new int[n][m];
int[][] bm=new int[n][m];

for(int i=0;i<n;i++){
for(int j=0;j<m;j++){
   dp[i][j]=scn.nextInt(); 
}
}
List<int[]> list = new ArrayList<>();
for(int i=0;i<n;i++){
    for(int j=0;j<m;j++){
        if(dp[i][j]==1){
            if(i+1<n && j+1<m){
                if(dp[i+1][j]==1 && dp[i][j+1]==1 && dp[i+1][j+1]==1){
                     bm[i][j]=1;
                     bm[i][j+1]=1;
                     bm[i+1][j]=1;
                     bm[i+1][j+1]=1;
                     list.add(new int[]{i+1,j+1});
                }else if(bm[i][j]==1){
                    continue;
                }else {
                    System.out.print(-1);
                    return;
                }
            }else if(bm[i][j]!=1){
                System.out.print(-1);
                return;
            }
        }
    }
}

for(int i=0;i<n;i++){
    for(int j=0;j<m;j++){
        if(bm[i][j]!=dp[i][j]){
            System.out.print(-1);
            return;
        }
    }
}
System.out.print(list.size()+"\n");
for(int[] sub:list){
    System.out.print(sub[0]+" "+sub[1]+"\n");
}
    } 

    }
