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.Scanner;

public class B1207 {

    public static void main(String[] args) {
        Scanner in = new Scanner(System.in);
        int R = in.nextInt();
        int C = in.nextInt();
        int[][] A = new int[R][C];
        for (int r=0; r<R; r++) {
            for (int c=0; c<C; c++) {
                A[r][c] = in.nextInt();
            }
        }
        int[][] B = new int[R][C];
        int K = 0;
        StringBuilder sb = new StringBuilder();
        for (int r=0; r<R-1; r++) {
            for (int c=0; c<C-1; c++) {
                if (A[r][c] == 1 && A[r+1][c] == 1 && A[r][c+1] == 1 && A[r+1][c+1] == 1) {
                    sb.append(r+1).append(' ').append(c+1).append('\n');
                    B[r][c] = B[r+1][c] = B[r][c+1] = B[r+1][c+1] = 1;
                    K++;
                }
            }
        }
        boolean ok = true;
        for (int r=0; r<R; r++) {
            for (int c=0; c<C; c++) {
                if (A[r][c] != B[r][c]) {
                    ok = false;
                }
            }
        }
        if (ok) {
            System.out.println(K);
            System.out.print(sb);
        } else {
            System.out.println("-1");
        }
    }

}
