#include<stdio.h>
#include<stdlib.h>
#include<string.h>

struct orz
{char s[1000];}a[50000];

int n,t;

char s[10][101],c[1000];

bool flag[10];

void dfs(int k)
{
	if(k>n){strcpy(a[++t].s,c);return;}
	int l=strlen(c);for(int i=1;i<=n;i++)
	if(!flag[i]){flag[i]=true;strcpy(c+l,s[i]);
	dfs(k+1);memset(c+l,0,sizeof(c+l));flag[i]=false;}
}

int cmp(const void *a,const void *b)
{return strcmp((*(orz *)a).s,(*(orz *)b).s);}

int main(int argc,char *argv[])
{
	freopen("substring.in","r",stdin);
	freopen("substring.out","w",stdout);
	int i;scanf("%d\n",&n);
	for(i=1;i<=n;i++)scanf("%s\n",s[i]);
	dfs(1);qsort(a+1,t,sizeof(orz),cmp);
	printf("%s\n",a[1].s);
	return 0;
}