#include<sstream>
#include<iostream>
#include<cstdio>
#include<cstdlib>
#include<cstring>
#include<cmath>
#include<string>
#include<vector>
#include<set>
#include<map>
#include<queue>
#include<numeric>
#include<functional>
#include<algorithm>
using namespace std;
#define INF (1<<29)
#define rep(i,n) for(int i=0;i<(int)(n);i++)
#define all(v) v.begin(),v.end()
#define uniq(v) v.erase(unique(all(v)),v.end())
#define indexOf(v,x) (find(all(v),x)-v.begin())




int main(){
	int n;
	cin>>n;
	priority_queue<string,vector<string>,greater<string> > pq;
	rep(i,n){
		string s;
		cin>>s;
		s+='~';
		pq.push(s);
	}
	string ans;
	while(!pq.empty()){
		string s=pq.top();pq.pop();
		if(s=="~")continue;
		ans+=s[0];
		s.erase(s.begin());
		pq.push(s);
	}
	cout<<ans<<endl;
	return 0;
}