//HSGS 2017-2020 - 10A1[A0] - #16
#include <iostream>
#include <ios>
#include <regex>
#include <array>
#include <string>
#include <cstdio>
#include <algorithm>
#include <iterator>
#include <cmath>
#include <iomanip>
#include <cstring>
#include <string>
#include <cstdlib>
#include <fstream>

using namespace std;

string processSet(string t);

int main()
{
    freopen("bclgold.inp","r",stdin);
    freopen("bclgold.out","w",stdout);
    unsigned long long int querycount;
    cin >> querycount; string queries = "";
    for (unsigned long long int i = 1 ; i <= querycount ; i++)
    {
        fflush(stdin);
        //char t = getchar();
        char t; cin >> t;
        queries = queries + t;
    };
    cout << processSet(queries);
}


string processSet(string t)
{
    string str = t, answer = "";
    transform(str.begin(),str.end(),str.begin(),::toupper);
    while (!str.empty())
    {
        char frontElement = *(str.begin()), backElement = str[str.length() - 1];
        if (frontElement < backElement)
        {
            answer = answer + frontElement;
            str.erase(0,1);
        }
        else
        {
            answer = answer + backElement;
            str.pop_back();
        }
    };
    return answer;
}