The fundamental operations in a double-ended queue D are : insertFirst (e) - Insert a new element e at the beginning of D. insertLast (e) - Insert a new element e at the end of D. removeFirst () - Remove and return the first element of D. removeLast () - Remove and return the last element of D. In an empty double-ended queue, the following operations are performed : insertFirst (10) insertLast (32) a ← removeFirst() insertLast (28) insertLast (17) a ←removeFirst() a ← removeLast () The value of a is _______.