//実装が重そうな問題はある程度考えてから書く
//初期化を忘れずに（特に二分探索とか）
//コーナーケースを考えて（特に場合分けとか）
//不可解すぎるバグは配列外参照（配列の長さ）を検討
#include <bits/stdc++.h>
#define YES "YES"
#define NO "NO"
#define YESNO OUT(three(solve(),YES,NO))
#define ECHO OUT(solve())
#define three(A,B,C) ((A)?(B):(C))
#define FOR(i,a,b)  for(LL i=(a);i< (LL)(b);i++)
#define EFOR(i,a,b) for(LL i=(a);i<=(LL)(b);i++)
#define RFOR(i,a,b) for(LL i=(a);i>=(LL)(b);i--)
#define REP(i,b) FOR(i,zero,b)
#define EREP(i,b) EFOR(i,zero,b)
#define RREP(i,b) RFOR(i,b,zero)
#define ALL(c) c.begin(),c.end()
#define UNIQUE(c) sort(ALL(c));c.erase(unique(ALL(c)),c.end())
#define MAX(c) (*max_element(ALL(c)))
#define MIN(c) (*min_element(ALL(c)))
#define MP make_pair
#define FI first
#define SE second
#define SI(x) (LL(x.size()))
#define PB push_back
#define DEBUG(a) OUT(a)
#define DEBUG2(a,b) OUT2(a,b)
#define cat cout << __LINE__ << endl
#define OUT(a) cout << (a) << endl
#define OUT2(a,b) cout << (a) <<" "<<(b) << endl
#define int LL
#define zero 0LL
using namespace std;
template<typename T> inline void maximize(T &a,T b){a=max(a,b);}
template<typename T> inline void minimize(T &a,T b){a=min(a,b);}
template<typename T> inline bool middle(T a,T b,T c){return b<=a && a<=c;}
template<class T> inline bool MX(T &l,const T &r){return l<r?l=r,1:0;}
template<class T> inline bool MN(T &l,const T &r){return l>r?l=r,1:0;}
typedef long long LL;
typedef double ld;
typedef LL ut;
typedef vector<ut> VI;
typedef vector<VI> VII;
typedef pair<ut,ut> pr;
typedef pair<ut,pr> ppr;
typedef vector<pr> Vpr;
typedef vector<ppr> Vppr;
typedef priority_queue<pr,Vpr,greater<pr> > PQ;
inline void outputVI(VI x){REP(i,SI(x)){cout << three(i," ","") << x[i];}OUT("");}
const int SIZE1=5*1e5+1000;
const int SIZE2=5010;
const int SIZE3=400;
const int SIZE=6050;
const LL p=7+1e9;
const LL INF=1LL<<60;
const long double EPS=1e-7;
string s;
ut N,M,K,X,L,Y;
// ut A,B,C,D,E,F,G,H,I,J,O,P,Q,R,T,U;
VI edges[SIZE];
LL vals[SIZE],nums[SIZE],maps[SIZE2][SIZE2],answer=zero;

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

////////////////////////////////////////////////////////////////////////////////////////////
void init(){
	
}
int A[SIZE];
string DP[SIZE];
int ind[SIZE];
int B[SIZE];
int ps(int x){
	if(s[x]=='a') return B[ind[x]];
	else return A[ind[x]];
}
void greedy(int now,string & ans,int& next){
	next=now+2;
	if(ps(now)<now){
		next=now+1;
		return;
	}
	FOR(i,now,2*N){
		if(next==i) return;
		if(now<=ps(i) && ps(i)<i && s[i]=='a') ans+='a'; 
		if(ps(i)<i) continue;
		if(s[i]=='a'){
			if(now==i) {
				ans="ab";	
				next=ps(i);
				return;
			}
		//	cout << now <<" " << next <<" " << i << endl;
		//	cout <<"OUT" << endl;
			assert(0);
		}else{
			ans+='b';
			next=ps(i)+1;
		}
	}
	
//	return ans;
}
string solve2(int now){
	if(now==2*N) return "";
	if(DP[now]!="") return DP[now];
	int next;
	string ans;
	greedy(now,ans,next);
	return DP[now]=max(solve2(now+1),ans+solve2(next));
}
LL solve(){
	cin >> N;
	cin >> s;
	int a=0,b=0;
	REP(i,s.size()){
		if(s[i]=='a'){
			ind[i]=a;
			A[a++]=i;
		}else{
			ind[i]=b;
			B[b++]=i;
		}
	}
	cout << solve2(0) << endl;
	return 0;
}
signed main(){
	solve();
	return 0;
}

Measured memory_bytes: 28800