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} 
#include <bits/stdc++.h>
using namespace std;
void print(vector<int> &A) {
  for (int i = 0; i < A.size(); i++) printf("%d ", A[i]);
  printf("\n");
}
void printm(vector<vector<int> > &m) {
  for (int i = 0; i < m.size(); i++) print(m[i]);
  printf("\n");
}
bool is_matrix_eq(vector<vector<int> > &A, vector<vector<int> > &B) {
  for (int i = 0; i < A.size(); i++)
    for (int j = 0; j < A[0].size(); j++)
      if (A[i][j] != B[i][j]) return false;
  return true;
}
int main() {
  int n, m;
  cin >> n >> m;
  vector<vector<int> > A(n, vector<int>(m));
  for (int i = 0; i < n; i++) {
    for (int j = 0; j < m; j++) {
      cin >> A[i][j];
    }
  }
  vector<pair<int, int> > ans;
  int k = 0;
  vector<vector<int> > B(n, vector<int>(m, 0));
  for (int i = 0; i < n - 1; i++) {
    for (int j = 0; j < m - 1; j++) {
      if (A[i][j] == 1 && A[i + 1][j] == 1 && A[i][j + 1] == 1 &&
          A[i + 1][j + 1] == 1) {
        ans.push_back(make_pair(i + 1, j + 1));
        B[i][j] = 1;
        B[i + 1][j] = 1;
        B[i][j + 1] = 1;
        B[i + 1][j + 1] = 1;
        k++;
      }
    }
  }
  if (!is_matrix_eq(A, B))
    cout << -1 << endl;
  else {
    cout << k << endl;
    for (int i = 0; i < ans.size(); i++)
      cout << ans[i].first << " " << ans[i].second << endl;
  }
  return 0;
}
