/**
 * code generated by JHelper
 * More info: https://github.com/AlexeyDmitriev/JHelper
 * @author majk
 */

#ifndef MAJK_LIB
#define MAJK_LIB

#include <vector>
#include <stack>
#include <iostream>
#include <fstream>
#include <unordered_map>
#include <unordered_set>
#include <map>
#include <iomanip>
#include <set>
#include <functional>
#include <algorithm>
#include <numeric>
#include <cassert>
#include <cmath>
#include <string>
#include <queue>
#include <array>
#include <bitset>
using namespace std;

#define x first
#define y second
typedef std::pair<int,int> pii; typedef long long ll; typedef unsigned long long ull; typedef unsigned int ui; typedef pair<ui,ui> puu;

template <typename T, typename U> std::istream&operator>>(std::istream&i, pair<T,U>&p) {i >> p.x >> p.y; return i;}
template<typename T>std::istream&operator>>(std::istream&i,vector<T>&t) {for(auto&v:t){i>>v;}return i;}
template <typename T, typename U> std::ostream&operator<<(std::ostream&o, const pair<T,U>&p) {o << p.x << ' ' << p.y; return o;}
template<typename T>std::ostream&operator<<(std::ostream&o,const vector<T>&t) {if(t.empty())o<<'\n';for(size_t i=0;i<t.size();++i){o<<t[i]<<" \n"[i == t.size()-1];}return o;}
template<typename T> using minheap = priority_queue<T, vector<T>, greater<T>>;
template<typename T> using maxheap = priority_queue<T, vector<T>, less<T>>;
ui logceil(ll x) { return x?8*sizeof(ll)-__builtin_clzll(x):0; }

namespace std { template<typename T,typename U>struct hash<pair<T,U>>{hash<T>t;hash<U>u;size_t operator()(const pair<T,U>&p)const{return t(p.x)^(u(p.y)<<7);}}; }
template<typename T,typename F>T bsh(T l,T h,const F&f){T r=-1,m;while(l<=h){m=(l+h)/2;if(f(m)){l=m+1;r=m;}else{h=m-1;}}return r;}
template<typename F> double bshd(double l,double h,const F&f,double p=1e-9){ui r=3+(ui)log2((h-l)/p);while(r--){double m=(l+h)/2;if(f(m)){l=m;}else{h=m;}}return (l+h)/2;}
template<typename T,typename F>T bsl(T l,T h,const F&f){T r=-1,m;while(l<=h){m=(l+h)/2;if(f(m)){h=m-1;r=m;}else{l=m+1;}}return r;}
template<typename F> double bsld(double l,double h,const F&f){ui r=200;while(r--){double m=(l+h)/2;if(f(m)){h=m;}else{l=m;}}return (l+h)/2;}
template<typename T> T gcd(T a,T b) { if (a<b) swap(a,b); return b?gcd(b,a%b):a; }


template<typename T>class vector2:public vector<vector<T>>{public:vector2(){} vector2(size_t a,size_t b,T t=T()):vector<vector<T>>(a,vector<T>(b,t)){}};
template<typename T>class vector3:public vector<vector2<T>>{public:vector3(){} vector3(size_t a,size_t b,size_t c,T t=T()):vector<vector2<T>>(a,vector2<T>(b,c,t)){}};
template<typename T>class vector4:public vector<vector3<T>>{public:vector4(){} vector4(size_t a,size_t b,size_t c,size_t d,T t=T()):vector<vector3<T>>(a,vector3<T>(b,c,d,t)){}};
template<typename T>class vector5:public vector<vector4<T>>{public:vector5(){} vector5(size_t a,size_t b,size_t c,size_t d,size_t e,T t=T()):vector<vector4<T>>(a,vector4<T>(b,c,d,e,t)){}};


#endif

class ESynchronizedSubsequence {
public:
    void solve(istream& cin, ostream& cout) {
        int N; cin >> N;
        string S; cin >> S;
        vector<int> A, B;
        int bal = 0;
        int last = 0;
        auto solve = [&](int x, int y) {
            if (A[x] < B[x]) {
                int j = -1;
                string ans;
                for (int i = x; i <= y; ++i) {
                    if (A[i] > j) { ans += "ab"; j = B[i]; }
                }
                return ans;
            } else {
                string ans = "";
                for (int i = x; i <= y; ++i) {
                    int j = i, k = i;
                    string cur = "";
                    while (j <= y || k <= y) {
                        if (j > y) {
                            cur += "b";
                            k++;
                        } else if (k > y) {
                            cur += "a";
                            j++;
                        } else if (A[j] < B[k]) {
                            cur += "a";
                            j++;
                        } else {
                            cur += "b";
                            k++;
                        }
                    }
                    ans = max(ans, cur);
                }
                return ans;
            }
        };
        vector<string> O;
        for (int i = 0; i < 2*N; ++i) {
            if (S[i] == 'a') {
                A.push_back(i);
                ++bal;
            } else {
                B.push_back(i);
                --bal;
            }
            if (bal == 0) {
                O.push_back(solve(last, B.size()-1));
                last = B.size();
            }
        }

        O.push_back(solve(last, B.size()-1));
        string Ans;
        for (int i = 0; i < O.size(); ++i) {
            bool ok = true;
            for (int j = i+1; j < O.size(); ++j) {
                if (O[i][0] == 'a') {
                    if (O[j][0] == 'b') ok = false;
                } else ok &= O[j] <= O[i];
            }
            if (ok) Ans += O[i];
        }
        cout << Ans << endl;
    }
};



int main() {
	ios_base::sync_with_stdio(false); cin.tie(nullptr); cout.tie(nullptr);
	ESynchronizedSubsequence solver;
	std::istream& in(std::cin);
	std::ostream& out(std::cout);
	solver.solve(in, out);
    return 0;
}



Measured memory_bytes: 3776