#include <stdio.h>
#include <string.h>
#include <malloc.h>
#include <ctype.h>
#include <stdlib.h>

const int m1 = 10, n1 = 20, N = 2;

int found(char **book, char *word, int *count, int n) {
    int i, j, f;
    for(i = 0, f = 1; (i < n) && (f); i++)
        if(strcmp(word, book[i]) == 0) {
            f = 0;
            count[i]++;
        }
    if(f) {
        strcpy(book[n], word);
        n++;
    }
    return n;
}

int input(char str[], int n1) {
    int c, i = 0;
    c = getchar();
    while((c != EOF) && (c != '\n')) {
        if(i > strlen(str))
            realloc(str, n1 * sizeof(char));
        str[i] = (char) c;
        c = getchar();
        i++;
    }
    if(c == '\n')
        return 1;
    else
        return 0;
}

int main() {
    char **book, *str, *word; int *count, i, j, n = 0;
    book = (char **) malloc(m1 * sizeof(char));
    for(i = 0; i < m1; i++)
        book[i] = (char *) malloc((n1 + 1) * sizeof(char));
    str = (char *) malloc((n1 + 1) * sizeof(char));
    word = (char *) malloc((n1 + 1) * sizeof(char));
    count = (int *) malloc(m1 * sizeof(char));
    for(i = 0; i < m1; i++)
        count[i] = 0;
    while(input(str, n1)) {
        for(i = 0, j = 0; str[i] != '\0'; i++)
            if((str[i] == ' ') || (str[i] == '\n')) {
                word[j] = '\0';
                n = found(book, word, count, n);
                j = 0;
            }
            else {
                word[j] = str[j];
                j++;
            }
    }
    for(i = 0; i < n; i++)
        if(count[i] >= N)
            fputs(book[i], stdout);
    return 0;
}