#include<iostream>
#include<string>
#include<vector>
#include<algorithm>
#include<fstream>
using namespace std;

ifstream fin(".in");

int n;
string s;
vector<string> v;

int main()
{
    #define cin fin
    cin>>n;
    for(int i=1;i<=n;++i)
    {

       cin>>s;
       v.push_back(s);
    }
    sort(v.begin(),v.end());
    for(auto x :v)
        cout<<x;
    return 0;
}