frekventen string

import java.util.*;

public class MostFrequentSubstring {

    public static void main(String[] args) {
        Scanner std = new Scanner(System.in);
        String str = std.nextLine();
        HashMap<String, Integer> tabela = new HashMap<>();
        String search;
        for (int i = 0; i < str.length(); i++) {
            for (int j = i + 1; j <= str.length(); j++) {
                search = str.substring(i, j);
                if (tabela.containsKey(search)) {
                    int g = tabela.get(search);
                    tabela.put(search, ++g);
                } else
                    tabela.put(search, 1);
            }
        }
        int max = 0;
        String maxSub = "";
        for (Map.Entry<String, Integer> entry : tabela.entrySet()) {
            if (entry.getValue() > max) {
                max = entry.getValue();
                maxSub = entry.getKey();
            } else if (entry.getValue() == max) {
                if (entry.getKey().length() > maxSub.length()) {
                    maxSub = entry.getKey();
                } else if (entry.getKey().length() == maxSub.length()) {
                    int n = 0;
                    for (int i = 0; i < entry.getKey().length(); i++) {
                        n += entry.getKey().charAt(i);
                    }
                    int m = 0;
                    for (int i = 0; i < maxSub.length(); i++) {
                        m += maxSub.charAt(i);
                    }
                    if (n < m)
                        maxSub = entry.getKey();
                }
            }
        }
        System.out.println(maxSub);
    }
}