Create a Python code that takes a floating-point number `score` between 0 and 100 as input and returns the letter grade based on the following scale:
- "A" for scores 90 and above.
- "B" for scores from 80 to 89.
- "C" for scores from 70 to 79.
- "D" for scores from 60 to 69.
- "F" for scores below 60.