#include <bits/stdc++.h>
using namespace std;
/*#include <ext/pb_ds/assoc_container.hpp>
#include <ext/pb_ds/tree_policy.hpp>
using namespace __gnu_pbds;
template<typename T> using gpp_set = tree<T, null_type, less<T>, rb_tree_tag, tree_order_statistics_node_update>;
template<typename T, typename L> using gpp_map = tree<T, L, less<T>, rb_tree_tag, tree_order_statistics_node_update>;
template<typename T> using gpp_multiset = tree<T, null_type, less_equal<T>, rb_tree_tag, tree_order_statistics_node_update>;*/
struct fast_ios { fast_ios(){ cin.tie(0); ios::sync_with_stdio(false); cout << fixed << setprecision(20); }; } fast_ios_;
#define FOR(i, begin, end) for(int i=(begin);i<(end);i++)
#define REP(i, n) FOR(i,0,n)
#define IFOR(i, begin, end) for(int i=(end)-1;i>=(begin);i--)
#define IREP(i, n) IFOR(i,0,n)
#define Sort(v) sort(v.begin(), v.end())
#define Reverse(v) reverse(v.begin(), v.end())
#define all(v) v.begin(),v.end()
#define SZ(v) ((int)v.size())
#define Lower_bound(v, x) distance(v.begin(), lower_bound(v.begin(), v.end(), x))
#define Upper_bound(v, x) distance(v.begin(), upper_bound(v.begin(), v.end(), x))
#define Max(a, b) a = max(a, b)
#define Min(a, b) a = min(a, b)
#define bit(n) (1LL<<(n))
#define bit_exist(x, n) ((x >> n) & 1)
#define debug(x) cout << #x << "=" << x << endl;
#define vdebug(v) cout << #v << "=" << endl; REP(i_debug, v.size()){ cout << v[i_debug] << ","; } cout << endl;
#define mdebug(m) cout << #m << "=" << endl; REP(i_debug, m.size()){ REP(j_debug, m[i_debug].size()){ cout << m[i_debug][j_debug] << ","; } cout << endl;}
#define pb push_back
#define f first
#define s second
#define int long long
#define INF 1000000000000000000
template<typename T> istream &operator>>(istream &is, vector<T> &v){ for (auto &x : v) is >> x; return is; }
template<typename T> ostream &operator<<(ostream &os, vector<T> &v){ for(int i = 0; i < v.size(); i++) { cout << v[i]; if(i != v.size() - 1) cout << endl; }; return os; }
template<typename T> void Out(T x) { cout << x << endl; }
template<typename T1, typename T2> void Ans(bool f, T1 y, T2 n) { if(f) Out(y); else Out(n); }

using vec = vector<int>;
using mat = vector<vec>;
using Pii = pair<int, int>;
using PiP = pair<int, Pii>;
using PPi = pair<Pii, int>;
using bools = vector<bool>;
using pairs = vector<Pii>;

//int dx[4] = {1,0,-1,0};
//int dy[4] = {0,1,0,-1};
//char d[4] = {'D','R','U','L'};

const int mod = 1000000007;
//const int mod = 998244353;
//#define Add(x, y) x = (x + (y)) % mod
//#define Mult(x, y) x = (x * (y)) % mod

void add_a(string &S, int i0, int i1, vector<string> &v){
    
    string x = "";
    vec id_A, id_B;
    FOR(i, i0, i1 + 1){
        if(S[i] == 'a') id_A.pb(i);
        else id_B.pb(i);
    }
    int ia = 0;
    while(ia < SZ(id_A)){
        x += "ab";
        int tmp = id_B[ia];
        while(ia < SZ(id_A) && id_A[ia] <= tmp) ia++;
    }

    if(SZ(v) > 0 && v.back()[0] == 'a') v.back() += x;
    else v.pb(x);
}

void add_b(string &S, int i0, int i1, vector<string> &v){
    string x = "";
    int now = 0;
    FOR(i, i0, i1 + 1){
        if(S[i] == 'b') now++;
        else now--;

        Max(x, string(now, 'b') + S.substr(i + 1, i1 - i));
    }
    v.pb(x);
}

signed main(){

    int N; cin >> N;
    string S; cin >> S;

    vector<string> v;
    int now = 0, i0 = 0;
    REP(i, 2 * N){
        if(S[i] == 'b') now++;
        else now--;

        if(now == 0){
            if(S[i0] == 'a') add_a(S, i0, i, v);
            else add_b(S, i0, i, v);
            i0 = i + 1;
        }
    }
    //vdebug(v);

    vector<string> ans;
    for(string x: v){
        while(SZ(ans) > 0 && ans.back() < x) ans.pop_back();
        ans.pb(x);
    }
    for(string x: ans) cout << x;
    cout << endl;

    return 0;
}


Measured memory_bytes: 384