#include<fstream>
#include<cstdlib>
#include<cstring>
using namespace std;
ifstream fin("substring.in");
ofstream fout("substring.out");
struct charing
{
	char str[101];
	charing()
	{
		memset(str,0,sizeof(str));
	}
};
int cmp(const void *a,const void *b)
{
	struct charing *c=(struct charing *)a;
	struct charing *d=(struct charing *)b;
	return strcmp(c->str,d->str);
}
int main()
{
	struct charing a[70];
	int n=0;
	fin>>n;
	for(int i=0;i<n;i++)
	{
		fin>>a[i].str;
	}
	qsort(a,n,sizeof(charing),cmp);
	for(int i=0;i<n;i++)
	{
		fout<<a[i].str;
	}
	fout<<endl;
	return (0);
}