I have read the question many times , still not getting the proper logic can you please tell me how exactly the things happening with explanation of test cases as well.
Question not clear to me
@1999atrijsharma
There are 3 students. Bhaiya will give 100% discount to 2 students using the initial number of discounts, i.e. 8 out of 10 will get used. We need atleast 2 more coupons to give discount to the third student. Now if the third student pay additional amount equivalent to Y=2 coupons, we will get a total of 4 coupons in hand, however we can not use them for giving discount as all 3 students have been considered (2 for getting discount and 1 for paying additional amount).
refer to this