// Wrongri-La Shower

#include <iostream>
#include <algorithm>

std::string S[50];

int main(){
    int N;
    std::cin >> N;

    int L = 0;
    for(int i=0;i<N;i++){
        std::cin >> S[i];
        L += S[i].size();
    }
    
    std::string T = "";
    std::string *first = S;
    for(int i=0;i<L;i++){
        std::sort(first, first+N, [](const std::string& lhs, const std::string& rhs){
                int l = std::min(lhs.size(), rhs.size());
                for(int i=0;i<l;i++){
                    if(lhs[i] != rhs[i]){
                        return lhs[i] < rhs[i];
                    }
                }
                return true;
        });

        T += (*first)[0];
        first->erase(0, 1);
        if(first->size() == 0){
            ++first; --N;
        }
    }

    std::cout << T << std::endl;
}