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.math.*;
import java.io.*; 
 public class B{
static int[] dx={-1,1,0,0};
static int[] dy={0,0,1,-1};
    static FastReader scan=new FastReader();
   public static PrintWriter out = new PrintWriter (new BufferedOutputStream(System.out));
  static ArrayList<Pair>es;
  static LinkedList<Integer>edges[];
   static boolean prime[];
   static void sieve(int n) 
    { 
        
        prime = new boolean[n+1]; 
        for(int i=0;i<n;i++) 
            prime[i] = true; 
          
        for(int p = 2; p*p <=n; p++) 
        { 
           
            if(prime[p] == true) 
            { 
                
                for(int i = p*p; i <= n; i += p) 
                    prime[i] = false; 
            } 
        } 
          
        
    }      
     public static int lowerBound(long[] array, int length, long value) {
        int low = 0;
        int high = length;
        while (low < high) {
            final int mid = (low + high) / 2;
            //checks if the value is less than middle element of the array
            if (value <= array[mid]) {
                high = mid;
            } else {
                low = mid + 1;
            }
        }
        return low;
    }
    public static int upperBound(long[] array, int length, long value) {
        int low = 0;
        int high = length;
        while (low < high) {
            final int mid = low+(high-low) / 2;
            if ( array[mid]>value) {
                high = mid ;
            } else {
                low = mid+1;
            }
        }
        return low;
    }
static long mod(long x,long y)
    {
        if(x<0)
            x=x+(-x/y+1)*y;
        return x%y;
    }    
    static boolean isPowerOfTwo(int n)
{
    if(n==0)
    return false;
 
return (int)(Math.ceil((Math.log(n) / Math.log(2)))) == 
       (int)(Math.floor(((Math.log(n) / Math.log(2)))));
}

  
   
static boolean isprime(long x)
           {
            for(long i=2;i*i<=x;i++)
                if(x%i==0)
                    return false;
                return true;
           }
static boolean vis[];

static int dist(int x1,int y1,int x2,int y2){
return Math.abs(x1-x2)+Math.abs(y1-y2);
}


    static long cuberoot(long x)
    {
        long lo = 0, hi = 1000005;
        while(lo<hi)
        {
            long m = (lo+hi+1)/2;
            if(m*m*m>x)
                hi = m-1;
            else
                lo = m;
        }
        return lo;
    }
     public static int log2(int N) 
    { 
  
        // calculate log2 N indirectly 
        // using log() method 
        int result = (int)(Math.log(N) / Math.log(2)); 
  
        return result; 
    } 
    static int n;
    static int arr[];
    static boolean is(int x)
    {
        PriorityQueue<Integer>pq=new PriorityQueue<Integer>();
        int l=x,r=n-1;
        //out.println(l+" "+r);
        that:while(l<=r)
        {
            //out.println("FUCK");
            if(arr[l]<=arr[r])
            {
               // out.println("FUCK");
                PriorityQueue<Integer>tmp=pq;
                while(!tmp.isEmpty())
                {
                    int mx=tmp.poll();
                    if(arr[l]<mx)
                      return false;
                }
                pq.add(arr[l]);
                l++;
            }
            else 
            {
                PriorityQueue<Integer>tmp=pq;
                while(!tmp.isEmpty())
                {
                    int mx=tmp.poll();
              //      out.println(mx);
                    if(arr[r]<mx)
                        return false;
                }
                pq.add(arr[r]);
                r--;
            }
        }
        
        return true;
    }
       static long gcd(long a, long b) {
    if(a!=0&&b!=0)
        while((a%=b)!=0&&(b%=a)!=0);
    return a^b;
}
    static long LCM(long a,long b){
    return (Math.abs(a*b))/gcd(a,b);
   }
public static void main(String[] args)  throws Exception 
{
//java.util.Scanner scan=new java.util.Scanner(new File("mootube.in"));
 //PrintWriter out = new PrintWriter (new FileWriter("mootube.out"));
 //scan=new FastReader("input.txt");
 //out = new PrintWriter ("output.txt");
 //System.out.println(~-1);
//System.out.println(2<<5);
    //System.out.println(0^1023);
//System.out.println(1023^1023);
    int tt=1;
// tt=scan.nextInt();
 outer:while(tt-->0)
 {
int n=scan.nextInt(),m=scan.nextInt();
int mat[][]=new int[n][m];
ArrayList<Pair>arr=new ArrayList<Pair>();
for(int i=0;i<n;i++)
    for(int j=0;j<m;j++)
        mat[i][j]=scan.nextInt();
    for(int i=0;i<n;i++)
        for(int j=0;j<m;j++)
            try{
            if(mat[i][j]*mat[i+1][j]*mat[i][j+1]*mat[i+1][j+1]>0)
            {
                mat[i][j]=2;
                mat[i+1][j]=2;
                mat[i][j+1]=2;
                mat[i+1][j+1]=2;
                arr.add(new Pair(i+1,j+1));
            }
        }
        catch(IndexOutOfBoundsException e)
        {}
        boolean flag=false;
for(int i=0;i<n;i++)
for(int j=0;j<m;j++)
    if(mat[i][j]==1)
     flag=true;
if(flag)
    out.println(-1);
else 
{
    out.println(arr.size());
    for(Pair p:arr)
    {
        out.print(p.x+" "+p.y);
        out.println();
    }
}
}
out.close();

}
static long binexp(long a,long n,long mod)
{
    if(n==0)
        return 1;
    long res=binexp(a,n/2,mod)%mod;
    res=res*res;
    if(n%2==1)
        return (res*a)%mod;
    else 
        return res%mod;
}
static class special implements Comparable<special>{
    int x;
    char id;
    special(int x,char id)
    {
        this.id=id;
       this.x=x;
    }
    public int compareTo(special o)
    {
        
        return x-o.x;
    }
   
}
 public static  long pow(long b, long e) {
            long r = 1;
            while (e > 0) {
                if (e % 2 == 1) r = r * b ;
                b = b * b;
                e >>= 1;
            }
            return r;
        }

private static void sort(long[] arr) {
        List<Long> list = new ArrayList<>();
        for (long object : arr) list.add(object);
        Collections.sort(list);
        for (int i = 0; i < list.size(); ++i) arr[i] = list.get(i);
    }
 public static class FastReader {
        BufferedReader br;
        StringTokenizer root;
        
 
        public FastReader() {
            br = new BufferedReader(new InputStreamReader(System.in));
        }
        FastReader(String filename)throws Exception
        {

            br=new BufferedReader(new FileReader(filename));
        }
 
        String next() {
            while (root == null || !root.hasMoreTokens()) {
                try {
                    root = new StringTokenizer(br.readLine());
                } catch (Exception addd) {
                    addd.printStackTrace();
                }
            }
            return root.nextToken();
        }
 
        int nextInt() {
            return Integer.parseInt(next());
        }
 
        double nextDouble() {
            return Double.parseDouble(next());
        }
 
        long nextLong() {
            return Long.parseLong(next());
        }
 
        String nextLine() {
            String str = "";
            try {
                str = br.readLine();
            } catch (Exception addd) {
                addd.printStackTrace();
            }
            return str;
        }
         public int[] nextIntArray(int arraySize) {
            int array[] = new int[arraySize];
 
            for (int i = 0; i < arraySize; i++) {
                array[i] = nextInt();
            }
 
            return array;
        }
}
public static class Pair implements Comparable<Pair>{
         int x;
        int  y;
        int id;
        public Pair(){}
        public Pair(int x1, int y1,int id) {
            x=x1;
            y=y1;
            this.id=id;
        }
        public Pair(int x1, int y1) {
            x=x1;
            y=y1;
        
        }
        @Override
        public int hashCode() {
            return (int)(x + 31 * y);
        }
        public String toString() {
            return x + " " + y;
        }
        @Override
        public boolean equals(Object o){
            if (o == this) return true;
            if (o.getClass() != getClass()) return false;
            Pair t = (Pair)o;
            return t.x == x && t.y == y;
        }
        public  int compareTo(Pair o)
        {
            if(o.x==x)
            return y-o.y;
        return x-o.x;
        }
}

}







