// C++ program to demonstrate the

// ordered set in GNU C++

#include <iostream>

using namespace std;

// Header files, namespaces,

// macros as defined above

#include <ext/pb_ds/assoc_container.hpp>

#include <ext/pb_ds/tree_policy.hpp>

#include <ext/pb_ds/detail/standard_policies.hpp>

using namespace __gnu_pbds;

template <class T>

using ordered_set = tree<T, null_type, less<T>, rb_tree_tag, tree_order_statistics_node_update>;

//use less_equal for multiset

// Driver program to test above functions

int main()

{

// Ordered set declared with name o_set

ordered_set<int> o_set;

// insert function to insert in

// ordered set same as SET STL

o_set.insert(5);

o_set.insert(1);

o_set.insert(2);

// Finding the second smallest element

// in the set using * because

// find_by_order returns an iterator

cout << *(o_set.find_by_order(1))

<< endl;

// Finding the number of elements

// strictly less than k=4

cout << o_set.order_of_key(4)

<< endl;

// Finding the count of elements less

// than or equal to 4 i.e. strictly less

// than 5 if integers are present

cout << o_set.order_of_key(5)

<< endl;

// Deleting 2 from the set if it exists

if (o_set.find(2) != o_set.end())

o_set.erase(o_set.find(2));

// Now after deleting 2 from the set

// Finding the second smallest element in the set

cout << *(o_set.find_by_order(1))

<< endl;

// Finding the number of

// elements strictly less than k=4

cout << o_set.order_of_key(4)

<< endl;

return 0;

}