#include    <iostream>
#include    <fstream>

using namespace std;

ifstream fin("bac.in");

int main()
{
    int ap = 0;
    int nr1, nr2;
    fin >> nr1;
    while(fin >> nr2)
    {
        if(nr1 == nr2)
            ap++;
        else
        {
            if(ap == 1)
                cout << nr1 << " ";
            ap = 0;
        }
        nr1 = nr2;
    }
    if(ap == 1)
        cout << nr1 << " ";
    return 0;
}