#include <bits/stdc++.h>
using namespace std;
#define FOR(i,m,n) for(int i=(m);i<(n);++i)
#define REP(i,n) FOR(i,0,n)
#define ALL(v) (v).begin(),(v).end()
using ll = long long;
constexpr int INF = 0x3f3f3f3f;
constexpr long long LINF = 0x3f3f3f3f3f3f3f3fLL;
constexpr double EPS = 1e-8;
constexpr int MOD = 998244353;
// constexpr int MOD = 1000000007;
constexpr int DY4[]{1, 0, -1, 0}, DX4[]{0, -1, 0, 1};
constexpr int DY8[]{1, 1, 0, -1, -1, -1, 0, 1};
constexpr int DX8[]{0, -1, -1, -1, 0, 1, 1, 1};
template <typename T, typename U>
inline bool chmax(T& a, U b) { return a < b ? (a = b, true) : false; }
template <typename T, typename U>
inline bool chmin(T& a, U b) { return a > b ? (a = b, true) : false; }
struct IOSetup {
  IOSetup() {
    std::cin.tie(nullptr);
    std::ios_base::sync_with_stdio(false);
    std::cout << fixed << setprecision(20);
  }
} iosetup;

int main() {
  int n; cin >> n;
  set<string> ng_words;
  REP(_, n) {
    string s; cin >> s;
    ng_words.emplace(s);
  }
  string ans = "";
  ans.reserve(n);
  REP(_, n) {
    array<int, 2> num{};
    for (const string& s : ng_words) {
      ++num[s.front() - 'a'];
    }
    const int les = distance(num.begin(), ranges::min_element(num));
    ans += 'a' + les;
    set<string> nxt;
    for (const string& e : ng_words) {
      if (e.front() == 'a' + les) nxt.emplace(e.substr(1));
    }
    ng_words.swap(nxt);
  }
  cout << ans << '\n';
  return 0;
}