Please maintain a Multiset, which stores integers and is able to support following operations:
(1) INSERT k – Insert an integer k into the multiset. k will fit in a 32-bit signed integer.
(2) COUNT k – Print how many k in the multiset.
(3) ERASEONE k – Delete exactly one k from the multiset. Do nothing if no k in multiset.
(4) ERASEALL k – Delete all k from the multiset. Do nothing if no k in multiset.
(5) CLEAR– Delete all elements in the multiset.
Hint : you may check cheatsheet to found out the usage of multiset