/* The following code example is taken from the book
 * "The C++ Standard Library - A Tutorial and Reference"
 * by Nicolai M. Josuttis, Addison-Wesley, 1999
 *
 * (C) Copyright Nicolai M. Josuttis 1999.
 * Permission to copy, use, modify, sell and distribute this software
 * is granted provided this copyright notice appears in all copies.
 * This software is provided "as is" without express or implied
 * warranty, and with no claim as to its suitability for any purpose.
 */
#include <iostream>
#include <string>
#include <algorithm>
using namespace std;

int main()
{
    istream_iterator<string> cinPos(cin);
    ostream_iterator<string> coutPos(cout," ");

    /* while input is not at the end of the file
     * - write every third string
     */
    while (cinPos != istream_iterator<string>()) {
        // ignore the following two strings
        advance (cinPos, 2);

        // read and write the third string
        if (cinPos != istream_iterator<string>()) {
            *coutPos++ = *cinPos++;
        }
    }
    cout << endl;
}