B"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 x 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. 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 . 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. The sequence of operations in the first example: "...