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} 
# -*- coding: utf-8 -*-
"""
Created on Sat Aug 24 13:48:42 2019

@author: Mridul Garg
"""
#n = 3
#m = 2
n, m = list(map(int, input().split()))
A = []
#B =! [[0]*m]*n
B = [[0 for i in range(m)] for j in range(n)] 
#B = []
#for i in range(n):
#    for j in range(m):
#        B
k = 0
opn = []

#for i in B:
#    print(i)

for _ in range(n):
    A.append(list(map(int, input().split(' '))))
    
#A = [[0,0], [0, 0], [0, 0]]

#print(A)
#print('HERE BITCHES')    
for i in range(n-1):
#    print('HERE')
    for j in range(m-1):
#        print('HERE TOO')
        if (A[i][j] == 1) and (A[i+1][j] == 1) and (A[i][j+1] == 1) and (A[i+1][j+1] == 1):
#            print(' REACHED ')
            B[i][j] = 1
            B[i+1][j] = 1
            B[i][j+1] = 1
            B[i+1][j+1] = 1
            k += 1
            opn.append([i+1, j+1])
#            for l in B:
#                print(l)
      
counter = 1
#for i in A and j in B:
#    if i != j:
#        counter = -1
#        print(-1)
#        break
#print(B)    

for i in range(n):
    if counter == -1:
        break
    for j in range(m):
        if A[i][j] != B[i][j]:
            counter = -1
            print(-1)
            break
    
if counter == 1:
    print(k)
    for i in opn:
        print(i[0], i[1])

#if A == B:
#    print(k)
#    for i in opn:
#        print(i[0, i[1]])
#    
#else:
#    print(-1)
#    print(k)
#    for i in opn:
#        print(i[0, i[1]])
    
           
        
    
#print(A)