#include<iostream>
#include<vector>
#include<string>
using namespace std;

string solve(string s) {
	int n = s.length();
	vector<int>pos(26, -1), num(n, 0);
	for (int i = 0; i < n; i++) {
		pos[s[i] - 'a'] = i;
	}
	for (int i = 0; i < n; i++) {
		for (int j = 0; j < 26; j++) {
			if (pos[j] > i) {
				num[i]++;
			}
		}
	}
	string ans;
	for (int i = 0; i < n; i++) {
		ans += 'a' + num[pos[s[i] - 'a']];
	}
	return ans;
}

int main() {
	int n = 0;
	cin >> n;
	string s,ans;
	cin >> s;
	for (int i = 0; i < (int)s.length(); i++) {
		string res = solve(s.substr(i));
		if (res > ans) {
			ans = res;
		}
	}
	cout << ans << endl;
	return 0;
}