#include<bits/stdc++.h>
using namespace std;


int main(){
    int N;
    priority_queue<string,vector<string>,greater<string> >Q;
    cin>>N;
    for(int i=0;i<N;i++){
        string str;cin>>str;
        Q.push(str);
    }

    string T;

    while(!Q.empty()){
        string s=Q.top();Q.pop();
        T+=s[0];
        if(s.size()==1)continue;
        else Q.push(s.substr(1,s.size()-1));
    }

    cout<<T<<endl;
    return 0;
}