#include <cstdio>
#include <cstring>
#include <cstdlib>
#include <vector>
#include <queue>
#include <string>
#include <functional>
#include <iostream>


using namespace std;

int main(){
	int n;scanf("%d",&n);
	string t,s;priority_queue<string,vector<string>, greater<string> > p;
	for(int i=0;i<n;i++){cin>>s;p.push(s);}
	while(p.size()){
		 
		char c=p.top()[0];
		t+=c;
		string tmp=p.top();tmp.erase(tmp.begin());p.pop();
		if(tmp.size())p.push(tmp);   
		
	} 
	 
	printf("%s\n",t.c_str());
	
	
	
	return 0;
}