Sudoku score engine

Development of scores engine in sudoku-app. Proposal is to have the best score to be the minimal one calculated by:

(number of actions (numbers input, numbers cleared) +
100*number of hints (penalty) +
number of seconds) x difficulty / 100 => rounded to nearest integer

difficulty = 1 for ultra hard, 2 for hard, 3 for medium, 4 for easy.

Ony other proposal is fine, but this is the general idea.