#define _CRT_SECURE_NO_WARNINGS

#include <cstdio>
#include <cstdlib>
#include <cstring>
#include <cmath>
#include <limits>
#include <ctime>
#include <cassert>
#include <map>
#include <set>
#include <iostream>
#include <memory>
#include <string>
#include <vector>
#include <algorithm>
#include <functional>
#include <sstream>
#include <stack>
#include <queue>
#include <numeric>
#include <iterator>
#include <bitset>
#include <unordered_map>
#include <unordered_set>

using namespace std;
#define FOR(i,n) for(int i = 0; i < (n); i++)
#define sz(c) ((int)c.size())
#define ten(n) ((int)1e##n)
using ll = long long;
using Pii = pair<int, int>;
using Pll = pair<ll, ll>;

template<typename ...> static inline int getchar_unlocked(void) { return getchar(); }
template<typename ...> static inline void putchar_unlocked(int c) { putchar(c); }
#define mygc(c) (c)=getchar_unlocked()
#define mypc(c) putchar_unlocked(c)
void reader(int& x) { int k, m = 0; x = 0; for (;;) { mygc(k); if (k == '-') { m = 1; break; }if ('0' <= k&&k <= '9') { x = k - '0'; break; } }for (;;) { mygc(k); if (k<'0' || k>'9')break; x = x * 10 + k - '0'; }if (m) x = -x; }
void reader(ll& x) { int k, m = 0; x = 0; for (;;) { mygc(k); if (k == '-') { m = 1; break; }if ('0' <= k&&k <= '9') { x = k - '0'; break; } }for (;;) { mygc(k); if (k<'0' || k>'9')break; x = x * 10 + k - '0'; }if (m) x = -x; }
int reader(char c[]) { int i, s = 0; for (;;) { mygc(i); if (i != ' '&&i != '\n'&&i != '\r'&&i != '\t'&&i != EOF) break; }c[s++] = i; for (;;) { mygc(i); if (i == ' ' || i == '\n' || i == '\r' || i == '\t' || i == EOF) break; c[s++] = i; }c[s] = '\0'; return s; }
int reader(string& c) { int i; for (;;) { mygc(i); if (i != ' '&&i != '\n'&&i != '\r'&&i != '\t'&&i != EOF) break; }c.push_back(i); for (;;) { mygc(i); if (i == ' ' || i == '\n' || i == '\r' || i == '\t' || i == EOF) break; c.push_back(i); }; return sz(c); }
template <class T, class S> void reader(T& x, S& y) { reader(x); reader(y); }
template <class T, class S, class U> void reader(T& x, S& y, U& z) { reader(x); reader(y); reader(z); }
template <class T, class S, class U, class V> void reader(T& x, S& y, U& z, V & w) { reader(x); reader(y); reader(z); reader(w); }
void writer(int x, char c) { int s = 0, m = 0; char f[10]; if (x<0)m = 1, x = -x; while (x)f[s++] = x % 10, x /= 10; if (!s)f[s++] = 0; if (m)mypc('-'); while (s--)mypc(f[s] + '0'); mypc(c); }
void writer(ll x, char c) { int s = 0, m = 0; char f[20]; if (x<0)m = 1, x = -x; while (x)f[s++] = x % 10, x /= 10; if (!s)f[s++] = 0; if (m)mypc('-'); while (s--)mypc(f[s] + '0'); mypc(c); }
void writer(const char c[]) { int i; for (i = 0; c[i] != '\0'; i++)mypc(c[i]); }
void writer(const string& x, char c) { int i; for (i = 0; x[i] != '\0'; i++)mypc(x[i]); mypc(c); }
void writer(const char x[], char c) { int i; for (i = 0; x[i] != '\0'; i++)mypc(x[i]); mypc(c); }
template<class T> void writerLn(T x) { writer(x, '\n'); }
template<class T, class S> void writerLn(T x, S y) { writer(x, ' '); writer(y, '\n'); }
template<class T, class S, class U> void writerLn(T x, S y, U z) { writer(x, ' '); writer(y, ' '); writer(z, '\n'); }
template<class T, class S, class U, class V> void writerLn(T x, S y, U z, V v) { writer(x, ' '); writer(y, ' '); writer(z, ' '); writer(v, '\n'); }
template<class T> void writerArr(T x[], int n) { if (!n) { mypc('\n'); return; }FOR(i, n - 1)writer(x[i], ' '); writer(x[n - 1], '\n'); }
template<class T> void writerArr(vector<T>& x) { writerArr(x.data(), (int)x.size()); }

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

template<class T> T gcd(T a, T b) { return b ? gcd(b, a % b) : a; }
template<class T> T lcm(T a, T b) { return a / gcd(a, b) * b; }
ll mod_pow(ll a, ll n, ll mod) {
	ll ret = 1;
	ll p = a % mod;
	while (n) {
		if (n & 1) ret = ret * p % mod;
		p = p * p % mod;
		n >>= 1;
	}
	return ret;
}
template<class T> T extgcd(T a, T b, T& x, T& y) { for (T u = y = 1, v = x = 0; a;) { T q = b / a; swap(x -= q * u, u); swap(y -= q * v, v); swap(b -= q * a, a); } return b; }
ll mod_inv(ll a, ll m) { ll x, y; extgcd<ll>(a, m, x, y); return (m + x % m) % m; }

vector<int> fidx(string s) {
	const int n = sz(s);
	vector<int> idx;
	int ac = 0, bc = 0;
	FOR(i, n) {
		if (s[i] == 'a') {
			idx.push_back(ac++);
		} else {
			idx.push_back(bc++);
		}
	}

	return idx;
}

string naive(string s) {
	string ret;
	const int n = sz(s);
	vector<int> idx = fidx(s);

	string ans;
	int binary = -1;
	FOR(F, (1 << (n - 1))) {
		string cur;
		FOR(i, n) {
			if ((1 << idx[i]) & F) {
				cur.push_back(s[i]);
			}
		}
		if (ans < cur) {
			binary = F;
			ans = cur;
		}
	}
	return ans;

}


string solvePlus(string s) {
	vector<int> idx = fidx(s);
	string ret = "ba";
	FOR(i, sz(s) / 2) {
		string cur;
		FOR(j, sz(s)) {
			if (idx[j] >= i)  cur.push_back(s[j]);
		}
		if (ret < cur) {
			ret = cur;
		}
	}

	return ret;
}

string solveMinus(string s) {
	vector<int> idx = fidx(s);
	string ret;
	FOR(i, sz(s)) {
		while (i < sz(s) && s[i] != 'a') i++;
		if (i == sz(s)) break;
		ret.push_back(s[i]);
		int cidx = idx[i];
		i++;
		while (idx[i] != cidx) i++;
		ret.push_back(s[i]);
	}

	return ret;
}

string solve(string s) {
	vector<string> vs;
	int cnt = 0;
	FOR(i, sz(s)) {
		if (cnt == 0) {
			vs.emplace_back();
		}
		if (s[i] == 'a') {
			cnt--;
		}
		if (s[i] == 'b') {
			cnt++;
		}
		vs.back().push_back(s[i]);
	}

	vector<string> vs2;
	FOR(i, sz(vs)) {
		bool strong = vs[i][0] == 'b';
		while (sz(vs2) && vs2.back()[0] == 'a' && strong) {
			vs2.pop_back();
		}
		vs2.push_back(vs[i]);
	}

	vector<string> vs3;
	string suffix;
	for (auto s : vs2) {
		string cur;
		if (s[0] == 'a') {
			cur = solveMinus(s);
			suffix += cur;
		} else {
			cur = solvePlus(s);
			while (sz(vs3) && vs3.back() < cur) {
				vs3.pop_back();
			}
			vs3.push_back(cur);
		}
	}

	string ans;
	for (auto s : vs3) ans += s;

	return ans + suffix;
}

void test() {
	int n = 16;
	string cur;
	FOR(i, n / 2) cur.push_back('a');
	FOR(i, n / 2) cur.push_back('b');
	do {
		string a1 = naive(cur);
		string a2 = solve(cur);
		if (a1 != a2) {
			cout << "?";
		}
	}
	while (next_permutation(cur.begin(), cur.end()));
}

int main() {
	// test();

	int n; reader(n);
	string s; reader(s);

	cout << solve(s) << endl;

	return 0;
}


Measured memory_bytes: 640