Let D be a data structure with two operations (i) and (i). Every (i) operation takes O(i) time and every (i) operation takes O(1) time. Assume that every (i) is followed by at least i operations of type (i). That is, if S is a sequence of m operations, then every operation (i) from S is followed by at least i operations (i). Using direct computations, prove that the amortized time of both operations is O(1)