Implement a balanced binary search tree.
Contains the description of operations on the tree, their number is not greater than 10^5
. Each line contains one of the following operations:
insert x - add the key x into the tree. If the key x is already in the tree, do nothing.
delete x - delete the key x from the tree. If the tree does not contain the key x, do nothing.
exists x - if the key x is in the tree, print "true", otherwise print "false".
All numbers are integers not greater than 10^9
by absolute value.
Print the result of all operations exists in format given in the sample output.