#include <iostream>
#include <vector>
#include <cstdio>
#include <string>
#include <cstring>
#include <algorithm>
using namespace std;
#define rep(i,n) for(int i=0;i<(n);i++)


int main(void){
	int n; cin >> n;
	vector<string> s(n);
	rep(i, n) cin >> s[i];
	string t;

	int sum = 0;
	rep(i, n){
		sum += s[i].size();
	}

	sort(s.begin(), s.end());
	rep(i, sum){
		rep(j, n){
			if(!s[j].empty()){
				t += s[j][0];
				s[j].erase(s[j].begin());
				break;
			}
		}
		sort(s.begin(), s.end());
	}
	cout << t << endl;
	return 0;
}