#include"bits/stdc++.h"

//#include<bits/stdc++.h>
using namespace std;
#define print(x) cout<<x<<endl;
#define rep(i,a,b) for(int i=a;i<b;i++)
#define REP(i,a) for(int i=0;i<a;i++)
typedef long long ll;
typedef pair<int, int> PI;
typedef pair<int, PI> V;
const ll mod = 10000000000;

int main() {
	int n;
	string s[52];
	cin >> n;
	REP(i, n) {	cin >> s[i];}
	string ans="";
	while (true) {
		string m="z";
		int mi=-1;
		REP(i, n) {
			if (s[i].empty())continue;
			if (m == "z"||m > s[i]) {
				m = s[i];
				mi = i;
			}
		}
		if (mi == -1)break;
		ans += m[0];
		s[mi].erase(s[mi].begin() + 0);
	}
	print(ans);
	return 0;
}