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.lang.*;
import java.lang.reflect.Array;
import java.io.*;
import java.math.*;
import java.text.DecimalFormat;
public class Prac{   
 
  
  
    static class InputReader {
 
		private final InputStream stream;
		private final byte[] buf = new byte[8192];
		private int curChar, snumChars;
 
		public InputReader(InputStream st) {
			this.stream = st;
		}
 
		public int read() {
			if (snumChars == -1)
	 			throw new InputMismatchException();
			if (curChar >= snumChars) {
				curChar = 0;
				try {
					snumChars = stream.read(buf);
				} catch (IOException e) {
					throw new InputMismatchException();
				}
				if (snumChars <= 0)
					return -1;
			}
			return buf[curChar++];
		}
 
		public int ni() {
			int c = read();
			while (isSpaceChar(c)) {
				c = read();
			}
			int sgn = 1;
			if (c == '-') {
				sgn = -1;
				c = read();
			}
			int res = 0;
			do {
				res *= 10;
				res += c - '0';
				c = read();
			} while (!isSpaceChar(c));
			return res * sgn;
		}
 
		public long nl() {
			int c = read();
			while (isSpaceChar(c)) {
				c = read();
			}
			int sgn = 1;
			if (c == '-') {
				sgn = -1;
				c = read();
			}
			long res = 0;
			do {
				res *= 10;
				res += c - '0';
				c = read();
			} while (!isSpaceChar(c));
			return res * sgn;
		}
 
		public int[] nia(int n) {
			int a[] = new int[n];
			for (int i = 0; i < n; i++) {
				a[i] = ni();
			}
			return a;
		}
 
		public String rs() {
			int c = read();
			while (isSpaceChar(c)) {
				c = read();
			}
			StringBuilder res = new StringBuilder();
			do {
				res.appendCodePoint(c);
				c = read();
			} while (!isSpaceChar(c));
			return res.toString();
		}
 
		public String nextLine() {
			int c = read();
			while (isSpaceChar(c))
				c = read();
			StringBuilder res = new StringBuilder();
			do {
				res.appendCodePoint(c);
				c = read();
			} while (!isEndOfLine(c));
			return res.toString();
		}
 
		public boolean isSpaceChar(int c) {
			return c == ' ' || c == '\n' || c == '\r' || c == '\t' || c == -1;
		}
 
		private boolean isEndOfLine(int c) {
			return c == '\n' || c == '\r' || c == -1;
		}
 
	}
    static PrintWriter w = new PrintWriter(System.out);
  
 
   
    public static void main(String[] args) throws IOException {   
        InputReader sc=new InputReader(System.in); 
        int n=sc.ni();
        boolean found=false;
        int m=sc.ni();
        int A[][]=new int[n+1][m+1];
        for(int i=1;i<=n;i++){
            for(int j=1;j<=m;j++){
                A[i][j]=sc.ni();
                
            }
        }
        int ans[][]=new int[n*m][2];
        int B[][]=new int[n+1][m+1];
        int count=0;
        for(int i=1;i<n;i++){
            for(int j=1;j<m;j++){
                if(A[i][j]==1&&A[i+1][j]==1&&A[i][j+1]==1&&A[i+1][j+1]==1){
                    ans[count][0]=i;
                    B[i][j]=1;
                    B[i+1][j]=1;
                    B[i][j+1]=1;
                    B[i+1][j+1]=1;
                    ans[count][1]=j;
                    count++;
                    
                }
            }
        }
        for(int i=1;i<=n;i++){
            for(int j=1;j<=m;j++){
                if(A[i][j]!=B[i][j]){
                    found=true;
                    break;
                }
            }
        }
        w.println((!found)?count:-1);
        if(!found){
        for(int i=0;i<count;i++){
            w.println(ans[i][0]+" "+ans[i][1]);
        }
        }
//        int t=sc.ni();
//        while(t-->0){
//            
//            int b=sc.ni();
//            int p=sc.ni();
//            int f=sc.ni();
//            int h=sc.ni();
//            int c=sc.ni();
//            int ans=0;
//            if(h>c){
//                if(b>=2*p){
//                    ans+=(p*h);
//                    b=b-(2*p);
//                }
//                else{
//                    ans+=(b/2)*h;
//                    b=0;
//                }
//                if(b>0){
//                    if(b>=2*f){
//                    ans+=(p*c);
//                    b=b-(2*f);
//                }
//                    else{
//                        ans+=(b/2)*c;
//                        b=0;
//                    }
//                }
//            }
//            else{
//                if(b>=2*f){
//                    ans+=(f*c);
//                    b=b-(2*f);
//                }
//                else{
//                    ans+=(b/2)*c;
//                    b=0;
//                }
//                if(b>0){
//                    if(b>=2*p){
//                    ans+=(p*h);
//                    b=b-(2*p);
//                }
//                    else{
//                        ans+=(b/2)*h;
//                        b=0;
//                    }
//                }
//            }
//            w.println(ans);
//        }
        
        w.close();
    }
}
