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} 
from bisect import *
from collections import *
from itertools import *
import functools
import sys
from math import *
from decimal import *
from copy import *
getcontext().prec = 30
MAX = sys.maxsize
MAXN = 10**5+10
MOD = 10**9+7
def isprime(n):
    n = abs(int(n))
    if n < 2:
        return False
    if n == 2: 
        return True    
    if not n & 1: 
        return False
    for x in range(3, int(n**0.5) + 1, 2):
        if n % x == 0:
            return False
    return True

def mhd(a,b):
    return abs(a[0]-b[0])+abs(b[1]-a[1])

def charIN(x= ' '):
    return(sys.stdin.readline().strip().split(x))

def arrIN(x = ' '):
    return list(map(int,sys.stdin.readline().strip().split(x)))

def eld(x,y):
    a = y[0]-x[0]
    b = x[1]-y[1]
    return (a*a+b*b)**0.5

def lgcd(a):
    g = a[0]
    for i in range(1,len(a)):
        g = math.gcd(g,a[i])
    return g

def ms(a):
    msf = -MAX
    meh = 0
    st = en = be = 0
    for i in range(len(a)):
        meh+=a[i]
        if msf<meh:
            msf = meh
            st = be
            en = i
        if meh<0:
            meh = 0
            be = i+1
    return msf,st,en

def ncr(n,r):
    num=den=1
    for i in range(r):
        num = (num*(n-i))%MOD
        den = (den*(i+1))%MOD

    return (num*(pow(den,MOD-2,MOD)))%MOD



def flush():
    return sys.stdout.flush()


def fac(n):
    ans = 1
    for i in range(1,n+1):
        ans*=i
        ans%=MOD
    return ans

'''*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*'''
def chk(i,j):
    x = []
    y = []
    z = []
    w = []
    for k in range(i-1,i+1):
        x.append(a[k][j-1:j+1])
    for k in range(i,i+2):
        y.append(a[k][j-1:j+1])
    for k in range(i-1,i+1):
        z.append(a[k][j:j+2])
    for k in range(i,i+2):
        w.append(a[k][j:j+2])
    #print(x,y,z,w)
    t = [[1,1],[1,1]]
    temp = [[i-1,j-1],[i,j-1],[i-1,j],[i,j]]
    p = [x==t,y==t,z==t,w==t]
    #print(p)
    if True in p:
        return temp[p.index(True)]
    else:
        return 0

n,m = arrIN()
a = []
temp = [0 for i in range(m)]
a.append(temp)
for i in range(n):
    a.append([0]+arrIN()+[0])
a.append(temp)
b = [[0 for i in range(m+2)] for j in range(n+2)]
ans = []
for i in range(1,n+1):
    for j in range(1,m+1):
        if a[i][j]==1:
            if chk(i,j)==0:
                print(-1)
                exit(0)
            else:
                ans.append(chk(i,j))
print(len(ans))
for i in ans:
    print(*i)














