#include <bits/stdc++.h>
using namespace std;
typedef long long int ll;
typedef unsigned int uint;
typedef unsigned char uchar;
typedef unsigned long long ull;
typedef pair<int, int> pii;
typedef pair<ll, ll> pll;
typedef vector<int> vi;

#define REP(i,x) for(int i=0;i<(int)(x);i++)
#define REPS(i,x) for(int i=1;i<=(int)(x);i++)
#define RREP(i,x) for(int i=((int)(x)-1);i>=0;i--)
#define RREPS(i,x) for(int i=((int)(x));i>0;i--)
#define FOR(i,c) for(__typeof((c).begin())i=(c).begin();i!=(c).end();i++)
#define RFOR(i,c) for(__typeof((c).rbegin())i=(c).rbegin();i!=(c).rend();i++)
#define ALL(container) (container).begin(), (container).end()
#define RALL(container) (container).rbegin(), (container).rend()
#define SZ(container) ((int)container.size())
#define mp(a,b) make_pair(a, b)
#define pb push_back
#define eb emplace_back
#define UNIQUE(v) v.erase( unique(v.begin(), v.end()), v.end() );
#define __builtin_popcount __builtin_popcountll

template<class T> bool chmax(T &a, const T &b) { if (a<b) { a=b; return 1; } return 0; }
template<class T> bool chmin(T &a, const T &b) { if (a>b) { a=b; return 1; } return 0; }
template<class T> ostream& operator<<(ostream &os, const vector<T> &t) {
    os<<"["; FOR(it,t) {if(it!=t.begin()) os<<","; os<<*it;} os<<"]"; return os;
}
template<class T> ostream& operator<<(ostream &os, const set<T> &t) {
    os<<"{"; FOR(it,t) {if(it!=t.begin()) os<<","; os<<*it;} os<<"}"; return os;
}
template<class S, class T> ostream& operator<<(ostream &os, const map<S, T> &t) {
    os<<"{"; FOR(it,t) {if(it!=t.begin()) os<<","; os<<*it;} os<<"}"; return os;
}
template<class S, class T> ostream& operator<<(ostream &os, const pair<S,T> &t) { return os<<"("<<t.first<<","<<t.second<<")";}
template<class S, class T> pair<S,T> operator+(const pair<S,T> &s, const pair<S,T> &t){ return pair<S,T>(s.first+t.first, s.second+t.second);}
template<class S, class T> pair<S,T> operator-(const pair<S,T> &s, const pair<S,T> &t){ return pair<S,T>(s.first-t.first, s.second-t.second);}

const int INF = 1<<28;
const double EPS = 1e-8;
const int MOD = 1000000007;


int T, n, m;
string s;

string solve(string s) {
    n = s.size() / 2;
    vi a, b;
    REP(i, 2 * n) {
        if (s[i] == 'a') a.push_back(i);
        if (s[i] == 'b') b.push_back(i);
    }
    a.push_back(2 * n);
    b.push_back(2 * n);
    vector<string> dp(n + 1), ma;
    int lastb = 0;
    RREP(i, n) {
        int c = 0, mx = 0;
        string ans = "";
        if (b[i] < a[i]) {
            for (int ja = i, jb = i; ja < n || jb < n;) {
                if (b[jb] < a[ja]) {
                    jb++;
                    ans.push_back('b');
                } else {
                    ja++;
                    ans.push_back('a');
                }
                if (ja == jb) {
                    ans += dp[ja];
                    break;
                }
            }
            lastb = i;
            dp[i] = max(ans, dp[i + 1]);
        } else {
            for (int ja = i; ; ja++) {
                if (b[i] < a[ja]) {
                    ans = dp[ja];
                    break;
                }
            }
            dp[i] = max("ab" + ans, dp[i + 1]);
        }
    }
    return dp[0];
}

int main(int argc, char *argv[]){
    ios::sync_with_stdio(false);
    while(cin >> n >> s){
        cout << solve(s) << endl;
    }
    return 0;
}


Measured memory_bytes: 14720