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.BufferedWriter;
import java.io.IOException;
import java.io.InputStream;
import java.io.InputStreamReader;
import java.io.OutputStreamWriter;
import java.io.PrintWriter;
import java.lang.reflect.Array;
import java.text.CollationKey;
import java.util.ArrayList;
import java.util.Arrays;
import java.util.BitSet;
import java.util.Collection;
import java.util.Collections;
import java.util.HashMap;
import java.util.HashSet;
import java.util.LinkedList;
import java.util.PriorityQueue;
import java.util.Queue;
import java.util.StringTokenizer;
import java.util.TreeMap;
import java.util.TreeSet;

public class Main {
	public static class edge {
		int u;
		int v;

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

		public double getdist(edge e) {
			return Math.sqrt((u - e.u) * (u - e.u) + (v - e.v) * (v - e.v));
		}

	}

	public static class UnionFind {
		int[] p, rank;
		boolean[] cyclic;

		public UnionFind(int N) {
			p = new int[N];
			rank = new int[N];
			// cyclic = new boolean[N];
			for (int i = 0; i < N; i++)
				p[i] = i;
		}

		public int findSet(int x) {
			return p[x] == x ? x : (p[x] = findSet(p[x]));
		}

		public boolean isunioned(int x, int y) {
			return findSet(x) == findSet(y);
		}

		public boolean union(int x, int y) {
			x = findSet(x);
			y = findSet(y);
			if (x == y) {
				return false;
			}
			if (rank[x] > rank[y])
				p[y] = x;
			else {
				p[x] = y;
				if (rank[x] == rank[y])
					++rank[y];
			}
			return true;
		}
	}

	static PrintWriter pw;
	static int n, m;
	static int[] rock, scis, pap;
	static int[][] acc;
	static long[][][] memo;

	public static boolean valid(int x, int y) {
		return acc[x][y] == 1;
	}

	public static void main(String[] args) throws IOException, InterruptedException {
		// FileWriter f = new FileWriter("C:\\Users\\Hp\\Desktop\\out.txt");
		// pw = new PrintWriter(System.in);
		// pw = new PrintWriter(System.in);
		pw = new PrintWriter(new BufferedWriter(new OutputStreamWriter(System.out)));
		Scanner sc = new Scanner(System.in);

		n = sc.nextInt();
		m = sc.nextInt();
		int[][] Arr = new int[n][m];
		acc = new int[n][m];
		int[] dx = new int[] { 0, -1, -1 };
		int[] dy = new int[] { 1, 0, 1 };
		for (int i = 0; i < n; i++)
			for (int j = 0; j < m; j++)
				Arr[i][j] = sc.nextInt();
		ArrayList<edge> ans = new ArrayList<Main.edge>();

		for (int i = 0; i < n; i++) {
			for (int j = 0; j < m; j++) {
				if (i == n - 1 || j == m - 1) {
					if (acc[i][j] != Arr[i][j]) {
						System.out.println(-1);
						return;
					}
					continue;
				}
				if (Arr[i][j] == 1) {
					if (acc[i][j] == 1) {
						if (Arr[i][j] == 1 && Arr[i + 1][j] == 1 && Arr[i][j + 1] == 1 && Arr[i + 1][j + 1] == 1) {
							ans.add(new edge(i + 1, j + 1));
							acc[i][j] = 1;
							acc[i + 1][j] = 1;
							acc[i][j + 1] = 1;
							acc[i + 1][j + 1] = 1;
						}
							continue;
						
					}
					ans.add(new edge(i + 1, j + 1));
					acc[i][j] = 1;
					acc[i + 1][j] = 1;
					acc[i][j + 1] = 1;
					acc[i + 1][j + 1] = 1;

				} else {
					if (acc[i][j] == 1) {
						System.out.println(-1);
						return;
					}
				}

			}
		}
		pw.println(ans.size());
		for (edge e : ans)
			pw.println(e.u + " " + e.v);
		pw.close();
	}

	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();
		}

	}

}
