#include <vector>
#include <list>
#include <map>
#include <set>
#include <deque>
#include <stack>
#include <queue>
#include <bitset>
#include <algorithm>
#include <functional>
#include <numeric>
#include <utility>
#include <sstream>
#include <iostream>
#include <iomanip>
#include <cstdio>
#include <cmath>
#include <cstdlib>
#include <cctype>
#include <string>
#include <cstring>
#include <ctime>

using namespace std;

typedef long long ll;
typedef unsigned long long ull;

static const double EPS = 1e-8;
static const double PI = 4.0 * atan(1.0);
static const double PI2 = 8.0 * atan(1.0);

#define REP(i,n)	for(int i=0;i<(int)n;++i)
#define ALL(c)		(c).begin(),(c).end()
#define CLEAR(v)	memset(v,0,sizeof(v))
#define MP(a,b)		make_pair((a),(b))
#define ABS(a)		((a)>0?(a):-(a))
#define FOR(i,s,n)	for(int i=s;i<(int)n;++i)

int N;
string S[50];

int main(int argc, char **argv) {
	cin >> N;
	int rem = 0;
	string res;
	REP(i, N) {
		cin >> S[i];
		rem += S[i].length();
		S[i] += 'z' + 1;
	}
	for (; rem > 0; --rem) {
		string mv = "";
		int mi = 0;
		REP(i, N) {
			if (mv == "" || S[i] < mv) {
				mi = i;
				mv = S[i];
			}
		}
		res += S[mi][0];
		S[mi] = S[mi].substr(1);
	}
	cout << res << endl;
	return 0;
}