/*
    _____
  .'     '.
 /  0   0  \
|     ^     |
|  \     /  |
 \  '---'  /
  '._____.'
*/
#include <bits/stdc++.h>
#include <ext/pb_ds/tree_policy.hpp>
#include <ext/pb_ds/assoc_container.hpp>

using namespace std;
using namespace __gnu_pbds;

struct chash
{
	int operator()(int x) const
	{
		x ^= (x >> 20) ^ (x >> 12);
		return x ^ (x >> 7) ^ (x >> 4);
	}
};

template<typename T> using ordered_set = tree<T, null_type, less<T>, rb_tree_tag, tree_order_statistics_node_update>;
template<typename T, typename U> using hashtable = gp_hash_table<T, U, chash>;
random_device(rd);
mt19937 rng(rd());

template<class T>
void readi(T &x)
{
	T input = 0;
	bool negative = false;
	char c = ' ';
	while (c < '-')
	{
		c = getchar();
	}
	if (c == '-')
	{
		negative = true;
		c = getchar();
	}
	while (c >= '0')
	{
		input = input * 10 + (c - '0');
		c = getchar();
	}
	if (negative)
	{
		input = -input;
	}
	x = input;
}
template<class T>
void printi(T output)
{
	if (output == 0)
	{
		putchar('0');
		return;
	}
	if (output < 0)
	{
		putchar('-');
		output = -output;
	}
	int aout[20];
	int ilen = 0;
	while(output)
	{
		aout[ilen] = ((output % 10));
		output /= 10;
		ilen++;
	}
	for (int i = ilen - 1; i >= 0; i--)
	{
		putchar(aout[i] + '0');
	}
	return;
}
template<class T>
void ckmin(T &a, T b)
{
	a = min(a, b);
}
template<class T>
void ckmax(T &a, T b)
{
	a = max(a, b);
}
template<class T, class U>
T nmod(T &x, U mod)
{
	if (x >= mod) x -= mod;
}
template<class T>
T randomize(T mod)
{
	return (uniform_int_distribution<T>(0, mod - 1))(rng);
}

#define y0 ___y0
#define y1 ___y1
#define MP make_pair
#define MT make_tuple
#define PB push_back
#define PF push_front
#define LB lower_bound
#define UB upper_bound
#define fi first
#define se second
#define debug(x) cerr << #x << " = " << x << endl;

const long double PI = 4.0 * atan(1.0);
const long double EPS = 1e-10;

#define MAGIC 347
#define SINF 10007
#define CO 1000007
#define INF 1000000007
#define BIG 1000000931
#define LARGE 1696969696967ll
#define GIANT 2564008813937411ll
#define LLINF 2696969696969696969ll
#define MAXN 6013

typedef long long ll;
typedef long double ld;
typedef pair<int, int> pii;
typedef pair<ll, ll> pll;
typedef pair<ld, ld> pdd;

int N, K;
int arr[MAXN], pref[MAXN];
int blocks[MAXN];
int partner[MAXN];
bitset<MAXN> typ;
vector<pii> idx[MAXN];
vector<bool> dp[MAXN];
vector<bool> ans;
bitset<MAXN> flag;

bool operator < (const vector<bool> &a, const vector<bool> &b)
{
	for (int i = 0; i < min(a.size(), b.size()); i++)
	{
		if (a[i] != b[i])
		{
			return a[i] < b[i];
		}
	}
	return (a.size() < b.size());
}
bool operator > (const vector<bool> &a, const vector<bool> &b)
{
	return b < a;
}

int32_t main()
{
	ios_base::sync_with_stdio(0);
	// cout << fixed << setprecision(10);
	// cerr << fixed << setprecision(10);
	// freopen ("file.in", "r", stdin);
	// freopen ("file.out", "w", stdout);
	cin >> N;
	N *= 2;
	string temps;
	cin >> temps;
	for (int i = 0; i < N; i++)
	{
		arr[i] = (temps[i] == 'a' ? 1 : -1);
		pref[i + 1] = pref[i] + arr[i];
	}
	for (int i = 1; i <= N; i++)
	{
		if (pref[i] == 0)
		{
			K++;
			blocks[K] = i - 1;
		}
	}
	blocks[0] = -1;
	for (int i = 1; i <= K; i++)
	{
		int lt = blocks[i - 1] + 1, rt = blocks[i];
		idx[i].resize((rt - lt + 1) / 2);
		int iter = 0;
		for (int j = lt; j <= rt; j++)
		{
			if (arr[j] == 1)
			{
				idx[i][iter].fi = j;
				iter++;
			}
		}
		iter = 0;
		for (int j = lt; j <= rt; j++)
		{
			if (arr[j] == -1)
			{
				idx[i][iter].se = j;
				iter++;
			}
		}
		// cerr << "block " << i << endl;
		for (pii p : idx[i])
		{
			partner[p.fi] = p.se;
			partner[p.se] = p.fi;
			// cerr << p.fi << ' ' << p.se << endl;
		}
		typ[i] = (bool) (idx[i][0].fi > idx[i][0].se);
	}
	for (int i = 1; i <= K; i++)
	{
		//if typ[i] is true, it's abababababab
		//if typ[i] is false, it's babababababa
		int lt = blocks[i - 1] + 1, rt = blocks[i];
		if (typ[i])
		{
			//babababa
			vector<bool> temp;
			for (int j = idx[i].size() - 1; j >= 0; j--)
			{
				flag[idx[i][j].fi] = true;
				flag[idx[i][j].se] = true;
				temp.clear();
				for (int k = lt; k <= rt; k++)
				{
					if (flag[k])
					{
						temp.PB(arr[k] - 1);
					}
				}
				if (temp > dp[i])
				{
					dp[i] = temp;
				}
				// for (bool b : dp[i])
				// {
				// 	cerr << (b ? 'b' : 'a');
				// }
				// cerr << endl;
			}
		}
		else
		{
			//ababababab
			for (int j = lt; j <= rt;)
			{
				dp[i].PB(0);
				dp[i].PB(1);
				j = partner[j];
				auto it = UB(idx[i].begin(), idx[i].end(), MP(j + 1, -INF));
				if (it == idx[i].end()) break;
				j = it -> fi;
			}
		}
	}
	// cerr << "our dps\n";
	for (int i = 1; i <= K; i++)
	{
		// for (bool b : dp[i])
		// {
		// 	cerr << (b ? 'b' : 'a');
		// }
		// cerr << endl;
		bool used = true;
		for (int j = i + 1; j <= K; j++)
		{
			for (int k = 0; k < dp[j].size() && k < dp[i].size(); k++)
			{
				if (dp[j][k] == 1 && dp[i][k] == 0)
				{
					used = false;
					break;
				}
				if (dp[j][k] == 0 && dp[i][k] == 1)
				{
					break;
				}
			}
			// if (dp[j] > dp[i]) used = false;
			if (!used)
			{
				break;
			}
		}
		if (used)
		{
			for (bool b : dp[i])
			{
				ans.PB(b);
			}
		}
	}
	for (bool b : ans)
	{
		cout << (b ? 'b' : 'a');
	}
	cout << '\n';
	// cerr << "time elapsed = " << (clock() / (CLOCKS_PER_SEC / 1000)) << " ms" << endl;
	return 0;
}


Measured memory_bytes: 896