#include <iostream>
#include <set>

using namespace std;

int main() {
    set<int> a {1,2,3,4};
    set<int> b {3,4,5,6};
    set<int> u(a);
    u.insert(b.begin(), b.end());
    for (set<int>::iterator i=u.begin() ; i != u.end(); ++i) {
        cout << *i << endl;
    }
	return 0;
}