#include <iostream>
#include <algorithm>
#include <string>
#include <vector>
#include <queue>
#include <stack>
#include <set>
#include <map>
#include <cstdio>
#include <cstdlib>
#include <cstring>
#include <cmath>
#include <numeric>
#define rep(x, to) for (int x = 0; x < (to); x++)
#define REP(x, a, to) for (int x = (a); x < (to); x++)
#define foreach(itr, x) for (typeof((x).begin()) itr = (x).begin(); itr != (x).end(); itr++)

using namespace std;

typedef long long ll;
typedef pair<int, int> PII;
typedef pair<long, long> PLL;

int N;
string s, ans;


bool comp(string a, string b) {
	return true;
}

priority_queue< string, vector<string>, greater<string> > que;


int main() {
	cin >> N;
	rep(i, N) {
		cin >> s;
		s += "}";
		que.push(s);
	}
	while (!que.empty()) {
		string cur = que.top(); que.pop();
		if (cur == "}") continue;
		ans += cur[0];
		cur = cur.substr(1);
		if (cur.size() > 0) {
			que.push(cur);
		}
	}
	cout << ans << endl;
	return 0;
}