frekventen

package com.company;
import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStreamReader;

class MapEntry<K extends Comparable<K>,E> implements Comparable<K> {

    K key;
    E value;

    public MapEntry (K key, E val) {
        this.key = key;
        this.value = val;
    }

    public int compareTo (K that) {
        @SuppressWarnings("unchecked")
        MapEntry<K,E> other = (MapEntry<K,E>) that;
        return this.key.compareTo(other.key);
    }

    public String toString () {
        return "(" + key + "," + value + ")";
    }
}

class SLLNode<E> {
    protected E element;
    protected SLLNode<E> succ;

    public SLLNode(E elem, SLLNode<E> succ) {
        this.element = elem;
        this.succ = succ;
    }

    @Override
    public String toString() {
        return element.toString();
    }
}

class CBHT<K extends Comparable<K>, E> {

    private SLLNode<MapEntry<K,E>>[] buckets;

    @SuppressWarnings("unchecked")
    public CBHT(int m) {
        buckets = (SLLNode<MapEntry<K,E>>[]) new SLLNode[m];
    }

    private int hash(K key) {
        return Math.abs(key.hashCode()) % buckets.length;
    }

    public SLLNode<MapEntry<K,E>> search(K targetKey) {
        int b = hash(targetKey);
        for (SLLNode<MapEntry<K,E>> curr = buckets[b]; curr != null; curr = curr.succ) {
            if (targetKey.equals(((MapEntry<K, E>) curr.element).key))
                return curr;
        }
        return null;
    }

    public void insert(K key, E val) {		// Insert the entry <key, val> into this CBHT.
        MapEntry<K, E> newEntry = new MapEntry<K, E>(key, val);
        int b = hash(key);
        for (SLLNode<MapEntry<K,E>> curr = buckets[b]; curr != null; curr = curr.succ) {
            if (key.equals(((MapEntry<K, E>) curr.element).key)) {
                curr.element = newEntry;
                return;
            }
        }
        buckets[b] = new SLLNode<MapEntry<K,E>>(newEntry, buckets[b]);
    }

    public void delete(K key) {
        int b = hash(key);
        for (SLLNode<MapEntry<K,E>> pred = null, curr = buckets[b]; curr != null; pred = curr, curr = curr.succ) {
            if (key.equals(((MapEntry<K,E>) curr.element).key)) {
                if (pred == null)
                    buckets[b] = curr.succ;
                else
                    pred.succ = curr.succ;
                return;
            }
        }
    }

    public String toString() {
        String temp = "";
        for (int i = 0; i < buckets.length; i++) {
            temp += i + ":";
            for (SLLNode<MapEntry<K,E>> curr = buckets[i]; curr != null; curr = curr.succ) {
                temp += curr.element.toString() + " ";
            }
            temp += "\n";
        }
        return temp;
    }

}

public class MostFrequentSubstring {

    public static void main (String[] args) throws IOException {
        CBHT<String,Integer> tabela = new CBHT<String,Integer>(300);
        BufferedReader br = new BufferedReader(new InputStreamReader(System.in));

        String word = br.readLine().trim();

        /*
         *
         * Vashiot kod tuka....
         *
         */
        int max=0;
        String maxString = "";
        for( int i=1; i <= word.length();i++){
            for(int j =0; j <= word.length()-i; j++){
                String podString = word.substring(j,j+i);
                //System.out.println(word.substring(j,j+i));
                if( tabela.search(podString) != null){
                    tabela.insert(podString,tabela.search(podString).element.value+1);
                    if( max == tabela.search(podString).element.value+1) {
                        if(podString.length() > maxString.length()) maxString = podString;
                        else if(podString.length() == maxString.length()){
                            if(podString.compareTo(maxString) == -1){
                                maxString = podString;
                            }
                        }
                        max = tabela.search(podString).element.value + 1;

                    }
                    if( max < tabela.search(podString).element.value+1){
                        max = tabela.search(podString).element.value + 1;
                        maxString = podString;
                    }

                }
                else {
                    tabela.insert(podString,1);
                    if( max <= 1) {
                        max = 1;
                        maxString = podString;
                    }

                }



            }
        }
        System.out.println(maxString);
        //System.out.println(tabela);



    }
}