#include <iostream>
#include <string>
#include <cmath>
#include<algorithm>
#include<stack>
#include<queue>
#include<map>
#include<set>
#include<iomanip>
#define _USE_MATH_DEFINES
#include <math.h>
#include <functional>
#include<complex>
using namespace std;

#define rep(i,x) for(ll i=0;i<x;i++)
#define repn(i,x) for(ll i=1;i<=x;i++)

typedef long long ll;
const ll INF = 1e17;
const ll MOD = 1000000007;
const ll MAX = 4000001;
const long double eps = 1E-14;

ll max(ll a, ll b) {
	if (a > b) { return a; }
	return b;
}

ll min(ll a, ll b) {
	if (a > b) { return b; }
	return a;
}

ll gcd(ll a, ll b) {
	if (b == 0) { return a; }
	if (a < b) { return gcd(b, a); }
	return gcd(b, a % b);
}

ll lcm(ll a, ll b) {
	return a / gcd(a, b) * b;
}

struct edge {
	ll ind;
	ll fr;
	ll to;
	ll d;
};

class mint {
	long long x;
public:
	mint(long long x = 0) : x((x% MOD + MOD) % MOD) {}
	mint operator-() const {
		return mint(-x);
	}
	mint& operator+=(const mint& a) {
		if ((x += a.x) >= MOD) x -= MOD;
		return *this;
	}
	mint& operator-=(const mint& a) {
		if ((x += MOD - a.x) >= MOD) x -= MOD;
		return *this;
	}
	mint& operator*=(const  mint& a) {
		(x *= a.x) %= MOD;
		return *this;
	}
	mint operator+(const mint& a) const {
		mint res(*this);
		return res += a;
	}
	mint operator-(const mint& a) const {
		mint res(*this);
		return res -= a;
	}
	mint operator*(const mint& a) const {
		mint res(*this);
		return res *= a;
	}

	mint pow(ll t) const {
		if (!t) return 1;
		mint a = pow(t >> 1);
		a *= a;
		if (t & 1) a *= *this;
		return a;
	}

	// for prime MOD
	mint inv() const {
		return pow(MOD - 2);
	}
	mint& operator/=(const mint& a) {
		return (*this) *= a.inv();
	}
	mint operator/(const mint& a) const {
		mint res(*this);
		return res /= a;
	}

	friend ostream& operator<<(ostream& os, const mint& m) {
		os << m.x;
		return os;
	}
};

mint pw(mint a, ll b) {
	if (b == 0) { return 1; }
	mint ret = pw(a, b >> 1);
	ret *= ret;
	if (b & 1) { ret *= a; }
	return ret;
}

typedef vector<ll> vll;
typedef vector<vector<ll>> vvll;
typedef vector<vector<vector<ll>>> vvvll;

typedef vector<mint> vmint;
typedef vector<vector<mint>> vvmint;
typedef vector<vector<vector<mint>>> vvvmint;

//////////////////////////////////////

string asen(string s) {
	ll acnt = 0;
	ll bcnt = 0;

	string ret;

	ll ad = -1;

	rep(i, s.size()) {
		if (s[i] == 'a') {
			if (ad == -1) { ret += 'a'; ad = acnt; }
			acnt++;
		}
		if (s[i] == 'b') {
			if (ad == bcnt) { ret += 'b'; ad = -1; }
			bcnt++;
		}
	}

	return ret;
}

string bsen(string s) {
	string ret;

	rep(i, s.size()) {
		if (s[i] == 'a') { continue; }

		ll acnt = 0;
		ll bcnt = 0;

		rep(j, i) {
			if (s[j] == 'a') { acnt++; }
			else { bcnt++; }
		}

		string now;
		for (ll j = i; j < s.size(); j++) {
			if (s[j] == 'b') { now += 'b'; }
			else {
				if (acnt == bcnt) { now += 'a'; }
				else { acnt++; }
			}
		}

		ret = max(ret, now);
	}

	return ret;
}


int main() {
	ll N;
	string s;
	cin >> N >> s;

	ll acnt = 0;
	ll bcnt = 0;
	vll ab(1, 0);
	rep(i, 2 * N) {
		if (s[i] == 'a') { acnt++; }
		else { bcnt++; }
		if (acnt == bcnt) { ab.push_back(i+1); }
	}
	ll M = ab.size() - 1;

	vector<string> lis;
	rep(i,M){
		string t = s.substr(ab[i], ab[i + 1] - ab[i]);
		if (t[0] == 'a') { lis.push_back(asen(t)); }
		else { lis.push_back(bsen(t)); }
	}

	string ans;

	rep(i, M) {
		bool b = 1;

		if (lis[i][0] == 'a') {
			for (ll j = i + 1; j < M; j++) { if (lis[j][0] == 'b') { b = 0; } }
		}
		else {
			for (ll j = i + 1; j < M; j++) { if (lis[j]>lis[i]) { b = 0; } }
		}

		if (b) { ans += lis[i]; }
	}
	cout << ans << endl;
}

Measured memory_bytes: 3776