#include<bits/stdc++.h>
using namespace std;
typedef long long int ll;
typedef pair<int,int> P;
const ll MOD=1000000007;
const ll INF=1000000010;
const ll LINF=4000000000000000010LL;
const int MAX=310;
const double EPS=1e-9;
int dx[4]={0,1,0,-1};
int dy[4]={1,0,-1,0};
int main(){
	int n;cin>>n;
	vector<string> s(n);
	for(int i=0;i<n;i++){
		cin>>s[i];
	}
	string ans="";
	while(1){
		int id,mi;mi=INF;
		for(int i=0;i<n;i++){
			if(s[i]=="")continue;
			if(mi>s[i][0]-'a'){
				mi=s[i][0]-'a';
				id=i;
			}
		}
		if(mi==INF)break;
		ans.push_back(s[id][0]);
		s[id].erase(0,1);
	}
	cout<<ans<<endl;
	return 0;
}