#include <bits/stdc++.h>
#include <ext/pb_ds/assoc_container.hpp>
#include <ext/pb_ds/tree_policy.hpp>

using namespace std ;
using namespace __gnu_pbds;

typedef tree<pair<int, int>, null_type, less<pair<int, int>>, rb_tree_tag, tree_order_statistics_node_update> ordered_set;

signed main(){
    int id = 0;
    ordered_set s;
    s.insert({0, id++});
    s.insert({0, id++});
    s.insert({0, id++});
    s.insert({0, id++});
    cout << int(s.size()) << endl;
    s.erase(s.lower_bound(make_pair(0, -1)));
    cout << int(s.size()) << endl;

}