#include <algorithm>
#include <iostream>
#include <iterator>
#include <set>

using namespace std;

int main() {
	set<int> foo = { 1, 2, 3 };

	for(auto it = begin(foo), finish = end(foo); it != finish; ++it) {
		foo.insert(*it * 2);
	}
	
	copy(cbegin(foo), cend(foo), ostream_iterator<int>(cout, " "));
}