#include "bits/stdc++.h"
#ifndef err
#define err(...)(void)0
#endif
using namespace std;
using ll = long long;
using ull = decltype(1ull);
template<class T>int size(T&&a) { return a.size(); }
#define REP(t,a)for(typename make_signed<decltype(a.second)>::type t=a.first,_l##t=a.second;t<_l##t;t++)
#define RREP(t,a)for(typename make_signed<decltype(a.second)>::type t=a.second-1,_l##t=a.first;t>=_l##t;t--)
template<class B>pair<int, B>make_pair(B b) { return{ 0,b }; }
#define rep(t,...)REP(t,make_pair(__VA_ARGS__))
#define rrep(t,...)RREP(t,make_pair(__VA_ARGS__))
#define all(a)begin(a),end(a)
#define rall(a)a.rbegin(),a.rend()
#define var(t, ...) t __VA_ARGS__;in,__VA_ARGS__;

void Calc();
int main() {
  ios::sync_with_stdio(false); cin.tie(nullptr);
  cin.exceptions(istream::failbit | istream::badbit);
  cout << fixed << setprecision(15); Calc(); cout.flush(); return 0;
}
template<class A>void amax(A&a, A b) { a = max(a, b); }
template<class A>void amin(A&a, A b) { a = min(a, b); }
template<class A>int comp(A a, A b) { return a < b ? 1 : b < a ? -1 : 0; }
struct Scanner {
  template<class A = string>A Next() { A a; cin >> a; return a; }
  template<class A = int>vector<A>Array(int n) { vector<A>a(n); for (A&i : a) cin >> i; return a; }
  string Line() const { string s; getline(cin, s); return s; }
  template<class A>Scanner&operator,(A&a) { a = Next<A>(); return *this; }
  template<class A>operator A() { return Next<A>(); }
}in;

/*---------------------------------------------------------------------*/

template<class ...T>tuple<T...>Init(T... t) { return{ t... }; }
template<class T>tuple<T> Init(T t) { return{ t }; }
template<int N, int...I>struct idx_seq : idx_seq<N - 1, 0, (I + 1)...> {};
template<int...I>struct idx_seq<0, I...> {};
template<class R, class T, int...I>R InitInternal(T&&a, idx_seq<0, I...>) { return R{ get<I>(a)... }; }
template<class T, class B, class...V>struct Vec {
  typedef Vec<T, V...>A; typedef vector<typename A::t>t; t nvec(B a, V...b) { return t(a, A().nvec(b...)); }
};
template<class T, class B>struct Vec<T, B> {
  using X = typename conditional<is_same<T, nullptr_t>::value, int, T>::type;
  typedef vector<X>t; t nvec(B a) { return t(a); }
};
template<class T, class ...C>struct Vec<T, tuple<C...>> {
  template<class A, class B>static pair<A, B> X(A, B);
  template<class...A>static tuple<A...> X(A...);
  using t = typename conditional < is_same<T, nullptr_t>::value, decltype(X(C{}...)), T > ::type;
  t nvec(tuple<C...> a) { return InitInternal<t>(a, idx_seq<sizeof...(C)>()); }
};
template<class T, class C>struct Vec<T, tuple<C>> {
  using X = typename conditional<is_same<T, nullptr_t>::value, C, T>::type;
  using t = X; t nvec(tuple<C> a) { return { get<0>(a) }; }
};
template<class T = nullptr_t, class...B> typename Vec<T, B...>::t nvec(B...b) { return Vec<T, B...>().nvec(b...); }



void Calc() {

  int n = in;
  auto s = in.Array<string>(n);

  map<char, int> m;
  rep(i, 2) {
    for (auto& i : s) {
      map<char, int> tmp;
      for (auto& j : i) {
        tmp[j]++;
      }
      for (auto& i : tmp) {
        if (m.find(i.first) == m.end()) {
          m[i.first] = i.second;
        }
        else {
          amin(m[i.first], i.second);
        }
      }
      for (auto& i : m) {
        amin(m[i.first], tmp[i.first]);
      }
    }
  }
  string ans;
  for (auto& i : m) {
    if (i.second > 0)ans += string(i.second, i.first);
  }
  cout << (ans) << endl;
}


Measured memory_bytes: 256