bacT4 sIII 3

#include <iostream>
#include <fstream>
using namespace std;
ifstream fin("bac.txt");

int main() {
    int x, last;
    fin >> last;
    int nrap = 1;
    while (fin >> x) {
        if (last == x) {
            nrap++;
        } else {
            if (nrap == 2) {
                cout << last << ' ';
            }
            nrap = 1;
        }
        last = x;
    }
    if (nrap == 2) {
        cout << last << ' ';
    }
    return 0;
}