#include <algorithm>
#include <climits>
#include <cmath>
#include <cstdio>
#include <cstdlib>
#include <ctime>
#include <iostream>
#include <sstream>
#include <functional>
#include <map>
#include <string>
#include <cstring>
#include <vector>
#include <queue>
#include <stack>
#include <deque>
#include <set>
#include <list>
#include <numeric>
using namespace std;
const double PI = 3.14159265358979323846;
const double EPS = 1e-12;
const int INF = 1<<25;
typedef pair<int,int> P;
typedef long long ll;
typedef unsigned long long ull;


int main(){
	int n;
	cin>>n;
	vector<string> s(n);
	for(int i = 0; i < n; i++) cin>>s[i];
	string t;
	while(true){
		int x = -1;
		for(int i = 0; i < n; i++){
			if(s[i].empty()) continue;
			if(x<0 || s[x][0]>s[i][0]) x = i;
		}
		if(x<0) break;
		t += s[x][0];
		s[x].erase(0, 1);
	}
	cout<<t<<endl;
	return 0;
}