#include <bits/stdc++.h>
using namespace std;
/*
Coded by 秦惜梦
The most attractive girl in the world
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*/

int n;
char s[6005];
int a[6005],b[6005],pos[6005],cnta,cntb;
string dp[6005];

int main(){
	scanf("%d",&n);
	scanf("%s",s+1);
	for(int i=1;i<=2*n;i++){
		if(s[i]=='a'){
			a[++cnta]=i;
			pos[i]=cnta;
		}else{
			b[++cntb]=i;
			pos[i]=cntb;
		}
	}
	for(int i=n;i>=1;i--){
		if(a[i]<b[i]){
			int to=0;
			for(int j=a[i];j<=b[i];j++){
				to=max(to,pos[j]);
			}
			dp[i]="ab"+dp[to+1];
		}else{
			int fk=i;
			while(fk<=n&&b[fk+1]<a[fk]){
				fk++;
			}
			for(int j=1;j<=2*n;j++){
				if(pos[j]>=i&&pos[j]<=fk){
					dp[i]+=s[j];
				}
			}
			dp[i]+=dp[fk+1];
		}
		dp[i]=max(dp[i],dp[i+1]);
	}
	cout<<dp[1]<<endl;
	return 0;
}

Measured memory_bytes: 14720