Fortress Sudoku 2014 - 1

I have decided to dabble in variants that I have not created before. So today we deal with a Fortress Sudoku. It is of an easy-medium difficulty level.

There is a Fortress marked by grey cells in the grid. Place numbers in the grid such that each row, column and 3x3 box contain the numbers 1 to 9. If a shaded cell and a white cell are orthogonally adjacent then the shaded cell has the greater value.