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} 
'''def check(x, y):
    global a, b
    if a[x][y]*a[x][y+1]*a[x+1][y]*a[x+1][y+1]==1:
        b[x][y], b[x][y+1], b[x+1][y], b[x+1][y+1] = 1, 1, 1,1
        return 1
    elif a[x][y]==b[x][y]: return 2
    return 3


n, m =map(int, input().split())
a= [list(map(int, input().split())) for i in range(n)]
#print(a)
b=[ [0]*m for i in range(n)]
k=0
kk=[]
z=1
for i in range(n-1):
    for j in range( m-1):
        ok=check(i, j)
        if ok==3: print(-1);z=0; break
        elif ok==1:
            k+=1
            kk.append([i+1, j+1])
        #print(i, j, ok)
    if z==0: k=-1; break
if k>=0:
    print(k)
    for i in kk:
        print(i[0], i[1])
'''

n, m =map(int, input().split())
a = [list(map(int, input().split())) for i in range(n)]
ans=[]
z=0

for i in range(n-1):
    for j in range(m-1):
        if a[i][j]*a[i][j+1]*a[i+1][j+1]*a[i+1][j]>0:
            a[i][j], a[i][j+1], a[i+1][j+1], a[i+1][j]=2,2,2,2
            ans.append([i+1, j+1])
            z+=1

ok = True

for i in range(n):
    if ok:
        for j in range(m):
            if a[i][j]==1: ok=False; print(-1); break

if ok:
    print(z)
    for k in ans:
        print(k[0], k[1])