ORDERSET  Order statistic set
https://codeforces.com/group/FLVn1Sc504/contest/274512/problem/X
English  Vietnamese 
In this problem, you have to maintain a dynamic set of numbers which support the two fundamental operations
 INSERT(S,x): if x is not in S, insert x into S
 DELETE(S,x): if x is in S, delete x from S
and the two type of queries
 KTH(S) : return the kth smallest element of S
 COUNT(S,x): return the number of elements of S smaller than x
Input
 Line 1: Q (1 ≤ Q ≤ 200000), the number of operations
 In the next Q lines, the first token of each line is a character I, D, K or C meaning that the corresponding operation is INSERT, DELETE, KTH or COUNT, respectively, following by a whitespace and an integer which is the parameter for that operation.
If the parameter is a value x, it is guaranteed that 0 ≤ x ≤ 10^{9}. If the parameter is an index k, it is guaranteed that 1 ≤ k ≤ 10^{9}.
Output
For each query, print the corresponding result in a single line. In particular, for the queries KTH, if k is larger than the number of elements in S, print the word 'invalid'.
Example
Input 8 I 1 I 1 I 2 C 0 K 2 D 1 K 1 K 2 Output 1 2 2 invalid
hide comments
fub_123:
20200930 12:13:18
pbds :) 

stormgate078:
20200902 15:13:28
Can be solved with modified AVL 

yaseenmollik:
20200806 12:26:01
Can be easily solve using pbds. But, should be solved using segment tree for practice purpose. 

amar_shukla1:
20200728 07:34:51
easy to solve by policy data structure 

fahimcp495:
20200602 00:05:53
it's worthy to solve after learning Treap 

anirudh_1999:
20200503 09:28:28
Getting TLE in java even after using segment trees with coordinate compression. 

pareksha:
20200429 07:53:08
Submitted solution > got TLE

Added by:  Jimmy 
Date:  20081028 
Time limit:  1.5s2s 
Source limit:  50000B 
Memory limit:  1536MB 
Cluster:  Cube (Intel G860) 
Languages:  All except: ERL JSRHINO NODEJS PERL6 VB.NET 
Resource:  Chess 