#include <bits/stdc++.h>

using namespace std;

#define FOR(i,a,b) for(int i=(a);i<(b);i++)
#define REP(i,n) FOR(i,0,n)
#define ALL(v) (v).begin(),(v).end()

template<typename A, typename B> inline bool chmax(A &a, B b) { if (a<b) { a=b; return 1; } return 0; }
template<typename A, typename B> inline bool chmin(A &a, B b) { if (a>b) { a=b; return 1; } return 0; }

typedef unsigned long long ull;
typedef long long ll;
typedef pair<int, int> pii;
typedef pair<ll, ll> pll;
typedef pair<pii, pii> P;

const ll INF = 1ll<<29;
const ll MOD = 1000000007;
const double EPS  = 1e-10;

int n;
string s[50];

int main() {
	cin >> n;
	REP(i, n) {
		cin >> s[i];
		while (s[i].size() < 50) s[i] += '~';
	}
	
	string ans = "";
	
	priority_queue<string, vector<string>, greater<string> > pq;
	REP(i, n) pq.push(s[i]);
	
	while (!pq.empty()) {
		string now = pq.top(); pq.pop();
		if (now[0] == '~') continue;
		
		ans += now[0];
		now.erase(now.begin());
		now += '~';
		pq.push(now);
	}
	
	cout << ans << endl;
	
	return 0;
}