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 multiLineArrayOfArraysPrint(arr):
    print('\n'.join([' '.join([str(x+1) for x in y]) for y in arr]))
def validRow(i):
    return 0<=i<n
def validCol(j):
    return 0<=j<m
def getAround(i,j):
    arr=[]
    for a in (-1,0):
        for b in (-1,0):
            x1=i+a;y1=j+b;x2=i+1+a;y2=j+b
            x3=i+a;y3=j+1+b;x4=i+1+a;y4=j+1+b
            xs=[x1,x2,x3,x4]
            ys=[y1,y2,y3,y4]
            ok=True
            for xx in xs:
                if not validRow(xx):
                    ok=False
            for yy in ys:
                if not validCol(yy):
                    ok=False
            if ok:
                arr.append([[x1,y1],[x2,y2],[x3,y3],[x4,y4]])
    return arr

n,m=[int(x) for x in input().split()]

a=[]
for _ in range(n):
    a.append([int(x) for x in input().split()])

b=[[0 for _ in range(m)] for __ in range(n)]

ans=[]
possible=True
for i in range(n):
    for j in range(m):
        if a[i][j]==1:
            ok2=False
            for coords in getAround(i,j):
#                print('i:{} j:{} coords:{}'.format(i,j,coords))
                ok=True
                for x,y in coords:
                    if a[x][y]==0:
                        ok=False
                if ok:
                    ans.append(coords[0])
                    ok2=True
                    break
            if ok2==False:
                possible=False
if possible:
    print(len(ans))
    multiLineArrayOfArraysPrint(ans)
    
#    test
#    for x,y in ans:
#        b[x][y]=1
#        b[x+1][y]=1
#        b[x][y+1]=1
#        b[x+1][y+1]=1
#    for i in range(n):
#        for j in range(m):
#            b[i][j]-=1
#    multiLineArrayOfArraysPrint(b)
else:
    print(-1)