#include <iostream>
#include <vector>
#include <string>
#include <set>

using namespace std;


int main(void){
    int n;
    cin >> n;
    vector<string> vectorforpair;
    set<string> myset;
    set<string> answer;

    for(int i=0;i<n;i++){
        string k;
        cin >> k;
        myset.insert(k);
    }
    set <string> :: iterator it = myset.begin();
    for (int i = 0; it !=myset.end(); i++, it++) {
        vectorforpair.push_back(*it);
    }
    for(int i=0;i<vectorforpair.size();i++)
    {
        for(int j=0;j<vectorforpair.size();j++)
        {
            if(myset.find(vectorforpair[i] + vectorforpair[j]) != myset.end()){
                answer.insert(vectorforpair[i] +vectorforpair[j]);
            }
        }
    }
    set <string> :: iterator it1 = answer.begin();
    for(int i=0;it1 != answer.end();i++,it1++){
        cout << *it1 << endl;
    }
    return 0;

}