Sandwich Sudoku

Sandwich Sudoku is a variation of Sudoku. The total of the numbers between the cell with the 1 and the cell with the 9 is shown by a number at the grid’s edge.

Rules: In each cell of the NxN grid, enter a number in the range 1–N. Each number must appear exactly once in each row and column, and in each grey and white block (but not in each region with a given number).
Additional rules: A number located at the edge of the grid shows the sum of the numbers between the cell with the 1 and the cell with the 9.