Instruction: Given the user's review, identify the user's sentiment from the listed options. Answer using one of the options.

Input:
I have attempted to use this machine several different times and each time my knees really ache after 2-3 days of use. I thought it was just me until I read the reviews.  I would not recommend this product if you have any problems with your knees, which I do not and I intend to keep it that way!

Options:
A: very positive
B: positive
C: neutral
D: negative
E: very negative
Answer: E: very negative