Hi,Today I came across one problem in hackerearth live contest,and I am confused that what is topic of this problem,I don't want solution I just want to which topic is of question.

Question: We have four number p,q,r,s and N<=10000 Where all numbers can be in range from 1 to N. But p<q<r<s so we have to find sum of all possible pair's gdc(p,q,r,s).

Thank you.