Master of Puzzles - Sohei Sudoku 200 Master Puzzles #4

The objective is to fill a 9x9 grid with digits so that each column, each row, and each of the nine 3x3 subgrids that compose the grid (also called "boxes", "blocks", or "regions") contains all of the digits from 1 to 9. The puzzle setter provides a partially completed grid, which for a well-posed puzzle has a single solution. Sohei Sudoku has four merged grids. Each grid has two overlapping areas. All grids must solved according to sudoku rules.