In this task, you need to answer the given multiple-choice question on the general math. Classify your answers into 'a', 'b', 'c', 'd', and 'e'.

Example Input: Problem: 8597 - ? = 7429 - 4358 
Options: a ) 3567 , b ) 6424 , c ) 6835 , d ) 5526 , e ) none of these
Example Output: d

Example Input: Problem: if [ x ] is the greatest integer less than or equal to x , what is the value of [ - 2.6 ] + [ 1.4 ] + [ 2.7 ] ? 
Options: a ) 0 , b ) 1 , c ) 2 , d ) 6 , e ) 7
Example Output: a

Example Input: Problem: if n is the product of integers from 1 to 20 inclusive what is the greatest integer k for which 2 ^ k is a factor of n ? . 
Options: a ) 10 , b ) 12 , c ) 15 , d ) 18 , e ) 20
Example Output:
d