#include <iostream>
#include <vector>
#include <algorithm>
using namespace std;
 
int main() {
	// your code goes here
    vector<string> vs = {"abc", "def"};
    //vs.reserve(vs.size()*2);
    vs.insert(vs.end(), vs.begin(), vs.end());
    for (auto &s : vs){
    	cout << ":" << s << endl;
    }
	return 0;
}