#include <iostream>
#include <string>
#include <vector>
#include <sstream>
#include <queue>
#include <algorithm>
#include <iomanip>
#include <map>
#include <set>
#include <math.h>
#include <stack>
#include <deque>
#include <numeric>
#include <cstring>
#include <cstdio>
#include <cstdlib>
#include <bitset>

#define all(v) v.begin(),v.end()
using namespace std;
typedef long long ll;
typedef unsigned long long ull;
typedef long double ld;
const ld epsylon = 1e-9;
typedef unsigned int ui;

int main()
{
	freopen("code.in","r",stdin);
	freopen("code.out","w",stdout);

	int n;
	char s[10001];
	scanf("%d\n",&n);
	cin >> s;

	string res;
	
	int fr = 0;
	int bk = n-1;
	while(fr<=bk) {
		if (s[fr] != s[bk]) {
			if (s[fr]<s[bk]) {
				res.push_back(s[fr++]);
			} else {
				res.push_back(s[bk--]);
			}
		} else { // equal letters
			int i;
			for (i = 1; fr + i < bk-i; i++) {
				if (s[fr+i]!=s[bk-i]) {					
					break;
				}
			}
			if (s[fr+i]<s[bk-i]) {
				res.push_back(s[fr++]);
			} else {
				res.push_back(s[bk--]);
			}
		}
	}
	
	cout << res << endl;
	return 0;
}