#include<iostream>
#include<queue>
using namespace std;
int N;
main()
{
	cin>>N;
	priority_queue<string,vector<string>,greater<string> >P;
	for(;N--;)
	{
		string s;cin>>s;P.push(s+'~');
	}
	while(!P.empty())
	{
		string s=P.top();P.pop();
		if(s[0]!='~')
		{
			cout<<s[0];
			P.push(s.substr(1));
		}
	}
	cout<<endl;
}