// ███▓▓▓▓▓▓▓▓▓╬╬╬╬╬╬╬╬╬╬╬╬╬╬╬╬╬▓▓▓╬╬╬╬╬╬▓█
// ███▓███████▓▓╬╬╬╬╬╬╬╬╬╬╬╬▓███▓▓▓▓█▓╬╬╬▓█
// ███████▓█████▓▓╬╬╬╬╬╬╬╬▓███▓╬╬╬╬╬╬╬▓╬╬▓█
// ████▓▓▓▓╬╬▓█████╬╬╬╬╬╬███▓╬╬╬╬╬╬╬╬╬╬╬╬╬█
// ███▓▓▓▓╬╬╬╬╬╬▓██╬╬╬╬╬╬▓▓╬╬╬╬╬╬╬╬╬╬╬╬╬╬▓█
// ████▓▓▓╬╬╬╬╬╬╬▓█▓╬╬╬╬╬╬╬╬╬╬╬╬╬╬╬╬╬╬╬╬╬▓█
// ███▓█▓███████▓▓███▓╬╬╬╬╬╬▓███████▓╬╬╬╬▓█
// ████████████████▓█▓╬╬╬╬╬▓▓▓▓▓▓▓▓╬╬╬╬╬╬╬█
// ███▓▓▓▓▓▓▓╬╬▓▓▓▓▓█▓╬╬╬╬╬╬╬╬╬╬╬╬╬╬╬╬╬╬╬▓█
// ████▓▓▓╬╬╬╬▓▓▓▓▓▓█▓╬╬╬╬╬╬╬╬╬╬╬╬╬╬╬╬╬╬╬▓█
// ███▓█▓▓▓▓▓▓▓▓▓▓▓▓▓▓╬╬╬╬╬╬╬╬╬╬╬╬╬╬╬╬╬╬╬▓█
// █████▓▓▓▓▓▓▓▓█▓▓▓█▓╬╬╬╬╬╬╬╬╬╬╬╬╬╬╬╬╬╬╬▓█
// █████▓▓▓▓▓▓▓██▓▓▓█▓╬╬╬╬╬╬╬╬╬╬╬╬╬╬╬╬╬╬╬██
// █████▓▓▓▓▓████▓▓▓█▓╬╬╬╬╬╬╬╬╬╬╬╬╬╬╬╬╬╬╬██
// ████▓█▓▓▓▓██▓▓▓▓██╬╬╬╬╬╬╬╬╬╬╬╬╬╬╬╬╬╬╬╬██
// ████▓▓███▓▓▓▓▓▓▓██▓╬╬╬╬╬╬╬╬╬╬╬╬█▓╬▓╬╬▓██
// █████▓███▓▓▓▓▓▓▓▓████▓▓╬╬╬╬╬╬╬█▓╬╬╬╬╬▓██
// █████▓▓█▓███▓▓▓████╬▓█▓▓╬╬╬▓▓█▓╬╬╬╬╬╬███
// ██████▓██▓███████▓╬╬╬▓▓╬▓▓██▓╬╬╬╬╬╬╬▓███
// ███████▓██▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓╬╬╬╬╬╬╬╬╬╬╬████
// ███████▓▓██▓▓▓▓▓╬╬╬╬╬╬╬╬╬╬╬╬╬╬╬╬╬╬╬▓████
// ████████▓▓▓█████▓▓╬╬╬╬╬╬╬╬╬╬╬╬╬╬╬╬▓█████
// █████████▓▓▓█▓▓▓▓▓███▓╬╬╬╬╬╬╬╬╬╬╬▓██████
// ██████████▓▓▓█▓▓▓╬▓██╬╬╬╬╬╬╬╬╬╬╬▓███████
// ███████████▓▓█▓▓▓▓███▓╬╬╬╬╬╬╬╬╬▓████████
// ██████████████▓▓▓███▓▓╬╬╬╬╬╬╬╬██████████
// ███████████████▓▓▓██▓▓╬╬╬╬╬╬▓███████████
// #pragma GCC optimize("Ofast")
// #pragma GCC target("sse,sse2,sse3,ssse3,sse4,popcnt,abm,mmx,tune=native")
// #pragma GCC optimize("unroll-loops")    
#include <iostream>
#include <vector>
#include <string>
#include <algorithm>
#include <cstdio>
#include <numeric>
#include <cstring>
#include <ctime>
#include <cstdlib>
#include <set>
#include <map>
#include <unordered_map>
#include <unordered_set>
#include <list>
#include <cmath>
#include <bitset>
#include <cassert>
#include <queue>
#include <deque>
#include <cassert>
#include <iomanip> 
#include <chrono>
#define pb push_back
#define x first
#define y second
#define mp make_pair
#define files(FILENAME) read(FILENAME); write(FILENAME)
#define read(FILENAME) freopen((string(FILENAME) + ".in").c_str(), "r", stdin)
#define write(FILENAME) freopen((string(FILENAME) + ".out").c_str(), "w", stdout)
using namespace std;
        
template<typename T1, typename T2>inline void chkmin(T1 &x, T2 y) { if (x > y) x = y; }
template<typename T1, typename T2>inline void chkmax(T1 &x, T2 y) { if (x < y) x = y; } 
template<typename T, typename U> inline ostream &operator<< (ostream &_out, const pair<T, U> &_p) { _out << _p.first << ' ' << _p.second; return _out; }
template<typename T, typename U> inline istream &operator>> (istream &_in, pair<T, U> &_p) { _in >> _p.first >> _p.second; return _in; }
template<typename T> inline ostream &operator<< (ostream &_out, const vector<T> &_v) { if (_v.empty()) { return _out; } _out << _v.front(); for (auto _it = ++_v.begin(); _it != _v.end(); ++_it) { _out << ' ' << *_it; } return _out; }
template<typename T> inline istream &operator>> (istream &_in, vector<T> &_v) { for (auto &_i : _v) { _in >> _i; } return _in; }
template<typename T> inline ostream &operator<< (ostream &_out, const set<T> &_s) { if (_s.empty()) { return _out; } _out << *_s.begin(); for (auto _it = ++_s.begin(); _it != _s.end(); ++_it) { _out << ' ' << *_it; } return _out; }
template<typename T> inline ostream &operator<< (ostream &_out, const multiset<T> &_s) { if (_s.empty()) { return _out; } _out << *_s.begin(); for (auto _it = ++_s.begin(); _it != _s.end(); ++_it) { _out << ' ' << *_it; } return _out; }
template<typename T> inline ostream &operator<< (ostream &_out, const unordered_set<T> &_s) { if (_s.empty()) { return _out; } _out << *_s.begin(); for (auto _it = ++_s.begin(); _it != _s.end(); ++_it) { _out << ' ' << *_it; } return _out; }
template<typename T> inline ostream &operator<< (ostream &_out, const unordered_multiset<T> &_s) { if (_s.empty()) { return _out; } _out << *_s.begin(); for (auto _it = ++_s.begin(); _it != _s.end(); ++_it) { _out << ' ' << *_it; } return _out; }
template<typename T, typename U> inline ostream &operator<< (ostream &_out, const map<T, U> &_m) { if (_m.empty()) { return _out; } _out << '(' << _m.begin()->first << ": " << _m.begin()->second << ')'; for (auto _it = ++_m.begin(); _it != _m.end(); ++_it) { _out << ", (" << _it->first << ": " << _it->second << ')'; } return _out; }
template<typename T, typename U> inline ostream &operator<< (ostream &_out, const unordered_map<T, U> &_m) { if (_m.empty()) { return _out; } _out << '(' << _m.begin()->first << ": " << _m.begin()->second << ')'; for (auto _it = ++_m.begin(); _it != _m.end(); ++_it) { _out << ", (" << _it->first << ": " << _it->second << ')'; } return _out; }
 
typedef long double base;        
typedef pair<int, int> point;

int n;
string s;
vector<string> rep;

int main() {
	ios::sync_with_stdio(0);
	srand(time(0));
	//read("input");
	cin >> n >> s;
	int balance = 0;
	string suf;
	for (auto c : s) {
		if (c == 'a') {
			++balance;
		} else {
			--balance;
		}
		suf += c;
		if (balance == 0) {
			vector<int> a, b;
			for (int i = 0; i < suf.size(); ++i) {
				if (suf[i] == 'a') {
					a.pb(i);
				} else {
					b.pb(i);
				}
			}
			if (suf[0] == 'a') {
				string res;
				int lst = -1;
				for (int i = 0; i < a.size(); ++i) {
					if (lst < a[i]) {
						lst = b[i];
						res += "ab";
					}
				}
				rep.pb(res);
			} else {
				string need = "";
				for (int i = 0; i < a.size(); ++i) {
					vector<bool> used(suf.size());
					for (int j = i; j < a.size(); ++j) {
						used[a[j]] = used[b[j]] = true;
					} 
					string res;
					for (int j = 0; j < suf.size(); ++j) {
						if (used[j]) {
							res += suf[j];
						}
					}
					chkmax(need, res);
				}
				rep.pb(need);
			}
			suf = "";
		}
	}
	reverse(rep.begin(), rep.end());
	string ans = "";
	for (auto s : rep) {
		string nans = s + ans;
		if (ans < nans) {
			ans = nans;
		}
	}
	cout << ans << endl;
}


Measured memory_bytes: 512