#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 = "";
	
	while (true) {
		bool ng = false;
		
		string mi = "~";
		int pos = -1;
		
		REP(i, n) if (s[i][0] != '~') {
			if (chmin(mi, s[i])) {
				mi = s[i];
				pos = i;
			}
		}
		
		if (pos == -1) break;
		
		ans += mi[0];
		s[pos].erase(s[pos].begin());
		s[pos] += '~';
	}
	
	cout << ans << endl;
	
	return 0;
}