#include <iostream>
#include <cstdio>
#include <cmath>
using namespace std;
int main(){
	freopen ("substring.in","r",stdin);
	freopen ("substring.out","w",stdout);
	int a,b,c,e,f,g,h,i,j,m,n[10][10]={0},l[10]={0};
	char d[10]={0},k;
	cin>>a;
	for (b=1;b<=a;b++)
	{
		cin>>d;
		for (m=0;d[m]!=0;m++)
		{
			n[b][m]=int (d[m])-96;
			l[b]++;
		}
	}
	for (c=1;c<=a;c++)
	{
		for (e=c+1;e<=a;e++)
		{
			for (f=0;;f++)
			{
				if(n[c][f]==0&&n[e][f]==0)
				{
					break;
				}
				if(n[c][f]>n[e][f]||n[e][f]==0)
				{
					for (g=0;g<=a-1;g++)
					{
						h=n[c][g];
						n[c][g]=n[e][g];
						n[e][g]=h;
					}
				}
			}
		}
	}
	for (i=1;i<=a;i++)
	{
		for (j=0;j<=l[i]-1;j++)
		{
			cout<<char (n[i][j]+96);
		}
	}
	return 0;
}