Letters Squares

Replace numbers 1-26 with letters a-z
Each square grid has a letter in the upper left corner
Click on the square and fill in one or two letters so that the letter after the letter is equal to the letter in the upper left corner of the square
When there are gray squares, no operation is required on the squares, and the letters filled in two consecutive squares on either side of the square cannot be duplicated
Completing the fill in the blanks for all squares within a limited time is considered successful