#include <cstdio>
#include <cstring>
#include <iostream>
#include <string>
#include <cmath>
#include <bitset>
#include <vector>
#include <map>
#include <set>
#include <queue>
#include <deque>
#include <algorithm>
#include <complex>
#include <unordered_map>
#include <unordered_set>
#include <random>
using namespace std;
typedef long long int ll;
typedef pair<int, int> P;

int main()
{
	int n;
	cin>>n;
	priority_queue<string, vector<string>, greater<string>> que;
	for(int i=0; i<n; i++){
		string s;
		cin>>s;
		while(s.size()<50) s+=('z'+1);
		que.push(s);
	}
	string ans;
	while(!que.empty()){
		string s=que.top(); que.pop();
		ans+=s[0];
		if(s[1]>'z') continue;
		string t=s.substr(1);
		t+=('z'+1);
		que.push(t);
	}
	cout<<ans<<endl;
    return 0;
}