Place each digit 1-9 exactly once in every row and column. Divide the grid into 3 snakes, which don't overlap and which collectively cover the entire grid. A snake is a 1-cell wide path of orthogonally connected cells with no branching. A snake may not touch itself, even diagonally. Cells separated by a black dot contain digits in a 2:1 ratio. Cells containing grey circles must contain odd digits. Thick borders between cells indicate those cells are a part of two different snakes. Adjacent cells along the same snake must contain digits that differ by exactly 4 or 5.