четвертый этаж

#include <iostream>
#include <string>
#include <sstream>
#include <cmath>
#include <algorithm>
#include <memory.h>
#include <stdio.h>
#include <stack>
#include <deque>
#include <queue>
#include <vector>
#include <set>
#include <iterator>
#include <map>
#include <iomanip>
#include <unordered_set>
#define int long long
#define pb push_back
#define double long double
#define endl "\n"
#define un unsigned
#define INF 1000000009
#define pii pair<int, int>
#define all(v) v.begin(), v.end()
using namespace std;

int n1;

istream& operator >> (istream& in, vector<pair<double, string>>& a)
{
    for (int i = 0; i < n1; i++)
    {
        in >> a[i].first >> a[i].second;
    }

    return in;
}

ostream& operator << (ostream& out, vector<pair<double, string>>& a)
{
    for (int i = n1 - 1; i > -1; i--)
    {
        out << a[i].first << " " << a[i].second << endl;
    }

    return out;
}


signed main()
{
    ios_base::sync_with_stdio();
    cin.tie(0);
    cout.tie(0);

    int n;
    cin >> n;

    set<int> st;

    for (int i = 1; i <= 300000; i++)
    {
        st.insert(i);
    }

    for (int i = 0; i < n; i++)
    {
        int a;
        cin >> a;

        if (a < 0)
        {
            st.insert(-a);
        }
        else
        {
            auto it = st.find(a);

            if (it == st.end())
            {
                it = st.upper_bound(a);
            }

            cout << *it << endl;

            st.erase(it);
        }
    }

    return 0;
}