#include<bits/stdc++.h>
using namespace std;
//common file for PBDS
#include<ext/pb_ds/assoc_container.hpp>
//including tree_order_statistics_node_update
#include<ext/pb_ds/tree_policy.hpp>
//namespace
using namespace __gnu_pbds;

//macro definition
#define ordered_set tree<int, null_type, less<int>, rb_tree_tag, tree_order_statistics_node_update>
int main(){

    //ordered set
    ordered_set st;
    //insert operation
    st.insert(5);
    st.insert(10);
    st.insert(1);
    st.insert(3);
    //st-> {1, 3, 5, 10}

    //find_by_order() return the iterator to the element at xth(0-based) position
    cout<<*(st.find_by_order(2));
    cout<<endl;

    //order_of_key() returns number of elements in set which are strictly less than x
    cout<<st.order_of_key(6);
    cout<<endl;
    st.insert(6);

    cout<<st.order_of_key(6);
    cout<<endl;


    return 0;
}