#include <bits/stdc++.h>
using namespace std;

using ll=int64_t;
#define int ll

#define FOR(i,a,b) for(int i=int(a);i<int(b);i++)
#define REP(i,b) FOR(i,0,b)
#define MP make_pair
#define PB push_back
#define ALL(x) x.begin(),x.end()
#ifdef MAROON_LOCAL
#define cerr (cerr<<"-- line "<<__LINE__<<" -- ")
#else
class CerrDummy{}cerrDummy;
template<class T>
CerrDummy& operator<<(CerrDummy&cd,const T&){
	return cd;
}
using charTDummy=char;
using traitsDummy=char_traits<charTDummy>;
CerrDummy& operator<<(CerrDummy&cd,basic_ostream<charTDummy,traitsDummy>&(basic_ostream<charTDummy,traitsDummy>&)){
	return cd;
}
#define cerr cerrDummy
#endif
#define REACH cerr<<"reached"<<endl
#define DMP(x) cerr<<#x<<":"<<x<<endl
#define ZERO(x) memset(x,0,sizeof(x))
#define ONE(x) memset(x,-1,sizeof(x))

using pi=pair<int,int>;
using vi=vector<int>;
using ld=long double;

template<class T,class U>
ostream& operator<<(ostream& os,const pair<T,U>& p){
	os<<"("<<p.first<<","<<p.second<<")";
	return os;
}

template<class T>
ostream& operator <<(ostream& os,const vector<T>& v){
	os<<"{";
	REP(i,(int)v.size()){
		if(i)os<<",";
		os<<v[i];
	}
	os<<"}";
	return os;
}

ll read(){
	ll i;
	scanf("%" SCNd64,&i);
	return i;
}

void printSpace(){
	printf(" ");
}

void printEoln(){
	printf("\n");
}

void print(ll x,int suc=1){
	printf("%" PRId64,x);
	if(suc==1)
		printEoln();
	if(suc==2)
		printSpace();
}

string readString(){
	static char buf[3341000];
	scanf("%s",buf);
	return string(buf);
}

char* readCharArray(){
	static char buf[3341000];
	static int bufUsed=0;
	char* ret=buf+bufUsed;
	scanf("%s",ret);
	bufUsed+=strlen(ret)+1;
	return ret;
}

template<class T,class U>
void chmax(T& a,U b){
	if(a<b)
		a=b;
}

template<class T,class U>
void chmin(T& a,U b){
	if(b<a)
		a=b;
}

template<class T>
T Sq(const T& t){
	return t*t;
}

#define CAPITAL
void Yes(bool ex=true){
	#ifdef CAPITAL
	cout<<"YES"<<endl;
	#else
	cout<<"Yes"<<endl;
	#endif
	if(ex)exit(0);
}
void No(bool ex=true){
	#ifdef CAPITAL
	cout<<"NO"<<endl;
	#else
	cout<<"No"<<endl;
	#endif
	if(ex)exit(0);
}

const ll infLL=LLONG_MAX/3;

#ifdef int
const int inf=infLL;
#else
const int inf=INT_MAX/2-100;
#endif

/*
signed main(){
	int n=read();
	string s=readString();
	vi pos(n,-1);
	int cnt[2]{};
	vi cor(n*2,-1);
	for(int i=n*2-1;i>=0;i--){
		int j=cnt[s[i]-'a']++;
		if(pos[j]==-1)
			pos[j]=i;
		else
			cor[i]=pos[j];
	}
	cerr<<cor<<endl;
	vector<string> ans(n*2+1);
	for(int i=n*2-1;i>=0;i--){
		
	}
}*/

signed main(){
	int n=read();
	string s=readString();
	vi pos(n,-1);
	int cnt[2]{};
	vi cor(n*2,-1);
	for(int i=n*2-1;i>=0;i--){
		int j=cnt[s[i]-'a']++;
		if(pos[j]==-1)
			pos[j]=i;
		else
			cor[i]=pos[j];
	}
	cerr<<cor<<endl;
	string ans;
	int t=n*2;
	for(int i=n*2-1;i>=0;){
		if(s[i]=='b'){
			int j=i,cur=0;
			while(1){
				cur+=(s[j--]-'a')*2-1;
				if(cur==0)break;
			}
			i=j;
			t=i+1;
		}else
			break;
	}
	cerr<<t<<endl;
	vector<string> dp(t+1);
	for(int head=t-1;head>=0;head--){
		if(s[head]=='b'&&cor[head]!=-1){
			vi use(n*2,0);
			string w;
			int right=cor[head],i=head;
			while(i<=right){
				if(s[i]=='b'){
					if(cor[i]!=-1){
						w+=s[i];
						use[cor[i]]=1;
						right=cor[i];
					}
				}else{
					if(use[i])
						w+=s[i];
				}
				i++;
			}
			cerr<<i<<" "<<w<<endl;
			w+=dp[i];
			chmax(ans,w);
		}
		dp[head]=ans;
	}
	cerr<<dp<<endl;
	for(int i=t;i<n*2;){
		if(s[i]=='a'){
			ans+="ab";
			i=cor[i];
		}else{
			i++;
		}
	}
	cout<<ans<<endl;
}


Measured memory_bytes: 16896