#include<iostream>
#include<vector>
#include<set>
#include<map>
#include<list>
#include<stack>
#include<queue>
#include<bitset>
#include<array>
#include<algorithm>
#include<cstdio>
#include<string>
#include<cstdlib>
#include<numeric>
#define D long long
#define U unsigned
using namespace std;
D n, m, a, b, d, e;
char c;
bool g, h;
string s;
D ans;
int main() {
	D i, j, k;
	U D t, u;
	vector<string> str;
	cin >> a;
	for (i = 0; i < a; i++) {
		cin >> s;
		str.push_back(s);
	}
	s = "";
	while (!str.empty()) {
		auto itt = str.begin();
		for (auto it = str.begin(); it != str.end(); it++) {
			if ((*it)[0] < (*itt)[0])
				itt = it;
		}
		s += (*itt)[0];
		itt->erase(itt->begin());
		if (itt->empty())
			str.erase(itt);
	}
	cout << s << endl;
}