/*
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 */
#include <iostream>
#include <complex>
#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 <stack>
#include <deque>
    
     
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; }
#define sz(c) (int)(c).size()
#define all(c) (c).begin(), (c).end()
#define rall(c) (c).rbegin(), (c).rend()
#define left left228
#define right right228
#define next next228
#define rank rank228
#define prev prev228
#define y1 y1228                                                         
#define read(FILENAME) freopen((FILENAME + ".in").c_str(), "r", stdin)
#define write(FILENAME) freopen((FILENAME + ".out").c_str(), "w", stdout)
#define files(FILENAME) read(FILENAME), write(FILENAME)
#define pb push_back
const string FILENAME = "input";
const int MAXN = 6001;


int n;
string s;
bool used[MAXN];


string get(string a) {
	vector<int> ga, gb;
	for (int i = 0; i < sz(a); i++) {
	 	if (a[i] == 'a') {
	 		ga.pb(i);
	 	} else {
	 		gb.pb(i);
	 	}
	}
	if (ga[0] < gb[0]) {
		string cur;
		cur = "ab";
		int last = gb[0];
		for (int i = 1; i < sz(ga); i++) {
			if (last < ga[i]) {
				cur += "ab";
				last = gb[i];
			}
		}
		return cur;
	} else {
		string opt;
		for (int i = sz(ga) - 1; i >= 0; i--) {
			memset(used, 0, sizeof(used));
			for (int j = i; j < sz(ga); j++) {
				used[ga[j]] = true;
			}
			for (int j = i; j < sz(gb); j++) {
				used[gb[j]] = true;
			}
			string b;
			for (int j = 0; j < sz(a); j++) {
				if (used[j]) {
					b += a[j];
				}
			}
			chkmax(opt, b);
		}
		return opt;
	}
}



string dp[MAXN];


int main() {
	ios_base::sync_with_stdio(false);
	cin.tie(0);
	cout.tie(0);
	//read(FILENAME);
	cin >> n;
	cin >> s;
	string cur;
	int bal = 0;
	vector<string> st;
	for (int i = 0; i <	2 * n; i++) {
		cur += s[i];
		if (s[i] == 'a') {
			bal++;
		} else {
			bal--;
		}
		if (bal == 0) {
			st.pb(get(cur));
			cur.clear();
		}
	}
	for (int i = sz(st) - 1; i >= 0; i--) {
		//cout << st[i] << endl;
		dp[i] = st[i];
		chkmax(dp[i], dp[i + 1]);
		chkmax(dp[i], st[i] + dp[i + 1]);
	}
	cout << dp[0] << '\n';
}



Measured memory_bytes: 10752